I have a Nikon D750 and a Fuji X-T1 and like them both. I find the D750 to be much superior when it comes to low light, high frames/second, better focusing and a much better choice of lenses and accessories. I personally like the colour rendering of Nikon over Fuji but I am sure others will disagree.
The Fuji is a great camera when I don't want to take all my gear but still want high quality images. The X-T1 with the 27mm pancake lens is second to none when it comes to easy carry around gear.
I use the Fuji as my second camera and my wife uses it when we are both out shooting. It has been said before on this thread, both formats are good for different things. Decide what makes the most sense for you and go for it.

The 50mm lens is not a good lens for portraits in that you would need to get to close to your subject possibly making them uncomfortable and affecting your end result. I learned 85mm to 105mm will give you adequate distance and maintain proper facial proportions for portraits. The Nikon 105 is in that upper price range that you don't want to go to. The 85/1.8 is likely the one you should get.
Enjoy your new lens.

I cannot speak to the D610 but I had a D3s and I changed to the D750. The D750 is as good or better than the D3s, it is much lighter and the articulated screen is a god send for us old people who have a hard time getting up when I am down on the ground taking photos. This way I don't have to go all the way down. The low light capabilities of the D750 are also as good and I think better than the D3s. The D3s had some features and the tank construction that I missed but I got over it soon enough.
The biggest difference in the added pixel count between the two cameras you are considering is that the extra pixels in the D610 actually add another lens equivalent to your camera in that you can crop much closer without losing the detail.
My recommendation of the two cameras you are considering is the D610 and I suggest the D750 if its added features have value to you.

I have absolutely zero to prove to you or anyone else. I am also not one to take cheap shots, it only shows ignorance. You are not worth my time.

I always find it interesting when someone can make such a definitive comment when they in fact appear just as uninformed. For the type of photography I take, the D800 is of little use to me. "Out of respect" what experience do you have with other genres of photography other than astro and landscape. For sport and some other types of photography, the D750 will blow the doors off the D800.

Both cameras are extremely competent tools for their intended uses. To say one is better than the other in every way is very narrow minded and uninformed.

To the original poster; look at what type of images you enjoy taking and how you use those images. There is enough information from previous posters to this one for you to make an informed decision. Without knowing that information, anyone who says one camera is better than the other is likely not the type of person you want to take advice from.

Both cameras are excellent for many things and each one has certain properties that will give them an edge for certain types of images. It is like comparing a car and a semi. Both will get you there but it just depends what you want to do along the way and how you want to do it.

Under what criteria would someone even say this. What makes a pro camera; what the heck is a "semi pro" camera; what about "prosumer", and I thought we are all consumers.

Many "pros" are going to mirrorless which don't hold a candle to either of these two cameras in my humble opinion.

People buy what they think is the best value for them. The D750 has many advantages over the D800 and the D800 has advantages over the D750. To say one is semipro and the other is consumer is an uninformed comment and doesn't add anything to help a person make an intelligent decision between the two.

I have trained for and judged many photography competitions. For most of the competitions I am involved with, impact has a value of 40%, Technical 30% and composition at 30%. Those cover the above list of 12 that I see. Impact is the subjective part of an image and it bears the greatest single % value. The technical and compositional side is, for the most part, fairly standard looking at the general guidelines of photography such as the rule of thirds and if you broke those rules, did it make the image better. Is the lighting, saturation, post processing etc. right for that image? Are their sensor spots, poles out of peoples heads or a cut off hand.

All images will have a different impact on the observer. As an example, ocean images likely have a very different impact on a judge from California than a judge from Montana, as it should. We are all different so it makes total sense to me that images can be rated differently by different judges.
In addition to that, it also depends on every other image that was submitted to the competition. I have seen mediocre images at best, win, because the competing images scored less.

Then there is the fact that judges are not infallible. They can get it wrong. Just because someone is a good photographer does not mean they will be a good judge because we all have our biases and we all have our genres of photography we are most comfortable with.

To minimize bias, many competitions have 5 judges with the highest and lowest score thrown out. Unfortunately, there are many competitions where a local single photographer will pick the winner. Those competitions can certainly not reflect the best image generally, just the best image as chosen by that person.

A great lens and my go-to lens with my D750, but it is not cheap nor is it real light. Still, you can't go wrong with it on any Nikon FF.

Are you people saying that everything on the internet is not true. Is Dr. Google not a real doctor. Albert Einstein said that 86% of everything on the internet is true.

With all due respect, I have a hard time believing a full frame camera will make anyone a better photographer. That is like saying if I buy better pots, I will be a better cook; or I will be a better driver if I have a better car.

As mentioned before, the big question is what type of images do you take. FX is better in low light because each pixel is larger than a similar MP DX camera, thus able to absorb more light. There is also a crop factor associated with a DX camera so if you tend to shoot more wide as opposed to long, the FX will work better with similar focal length lenses and lastly, if all of your lenses are FX then there can be a considerable cost in switching over.
The quality of sensors do not really differ based on size so that shouldn't be a factor. Certainly the quality of the image can differ with the size depending on the conditions you are shooting.
I like to shoot wide and I shoot a lot with existing light so an FX makes the most sense for me, but there are drawbacks with an FX of which many were mentioned above. They are heavier, they can be much more expensive and if you often shoot wildlife the crop factor on the DX will probably suit you better.

I have the Nikon D750 and a full kit of lenses and speedlights. I bought a used Fuji X-T1 and the 18-55 lens as a second camera for when I don't want to carry my Nikon kit. I quite enjoy having it and my wife uses it regularly when she wants a camera. Just remember, the IQ will not be as good as your Canon kit and there are restrictions, especially at the extremes but it is more than adequate as a second camera or a first camera depending on what you shoot.
One consideration you might want to take is to add a 27mm F2.8 pancake lens as an additional alternative for when you really do want to lighten your load. It takes very little room and and is not that expensive.
Good luck with your decision.

I believe if you use your Canon lenses on the Sony with an adaptor, you must focus manually. The argument of prefocusing for street photography is lost if you use back button focus. I have a D750 and I often shoot at its extremes, ISO 6400 plus, and am always amazed at the image quality this camera puts out.

I think it really depends on what type of photography you shoot. If you walk around, looking for birds, then it is one lens and if you walk around while travelling in cities it is another.
I typically shoot wide instead of long so my walk around lens is the Nikon 24-70 2.8. I have the one that is not VR but at those focal lengths you likely do not need VR anyway. You should be able to pick up one at a good price now that the new VR just came out.
With a camera like the D810, I would suggest you buy the best lens quality you can afford so you can take advantage of the sensor that you have.

I just came back from Ireland in June. Generally, the rain in Ireland is not a torrential downpour but a light to medium steady rain and for us, although it rained every day for three weeks, it stopped many times throughout the day.

I have a Nikon D750 and all I did was have a facecloth from the hotel with me all the time to wipe off any water on the camera, a lens cloth for the glass and always kept on the lens hood. I had my camera inside my jacket when I wasn't shooting. I did have a rain cover for my camera bag which I used twice when I went running for cover. When it was pouring and windy outside, I went inside to shoot somewhere until it let up a bit which usually wasn't very long. The rain covers mentioned above could work but I didn't use one and had no problem. Since they are inexpensive, it is probably worthwhile taking it.

Ireland is a spectacular country with amazing opportunities for great images but blue sky can be a rarity. No one ever goes to Ireland for the weather. Lightroom worked for me to remove some of the mist and I tried to take shots without the sky as often as I could because grey sky with no texture does not do much for a great photo. I have attached one if you are interested. Good luck on your travels.

There is a saying I just love. "If you are lucky enough to be Irish .... your're lucky enough.

Kylemore Abbey