SteveR Loc: Michigan

If you really are interested in low light capability, look at either the D500 or D7500. I know those are crop sensor cameras, but they will beat even the D850 in low light capability. Of course the flagship D5 will kill any other Nikon available for low light, but you'll pay for it. I've not looked at the specs of the D3, D4 or D4s (as mentioned previously) so maybe those would be good alternatives since you could probably pick up a good used model.

yssirk123 Loc: New Jersey

Completely agree with with astacus. The D3S was my all time favorite camera, and my daughter is still using it to shoot weddings. Simply beautiful noise-free images SOC, and with the ability to print large despite the relatively small native 12MP files.

jacklewis014

I have a D4 and it is awesome. I am looking for another D4 as a backup, instead of saving for a new D5. I shoot a lot of indoor sports - low light and fast action. This camera is amazing at high ISO, wide open with fast shutter.

camerapapi Loc: Miami, Fl.

"Sooo What say you?"

I own a D610. It fits my needs but that is me. You seem to need something that will give you a higher ISO than 6400 with perhaps better AF and a faster shooting rate. By the way, native ISO in the D610 is ISO 100 which is pretty nice for portraits and landscape photography.
I am familiar with the D750 but not with the D850. All I hear and read about the D850 is very positive and agree with you, the cost of one of those bodies is high.
The majority of your lenses are for the DX format. The D500, not familiar with it but everything I hear about it is also very positive, shoots at a higher firing rate, has an excellent AF and from what I know its low light performance is impressive. Getting a very good wide angle for DX format should be no issues buying the excellent Tokina 11-16 f2.8, a lens that from everything I know about it has excellent resolution and a f2.8 aperture which is important for someone like you that works often in low light.
My 2 cents.

DaveC1 Loc: South East US

This has been posted before, but you may find it useful when comparing different cameras ISO performance:

http://www.photonstophotos.net/Charts/PDR.htm

mborn Loc: Massachusetts

I have a D810 and a D500. I use each for different purposes

bpulv Loc: Buena Park, CA

First of all, no DSLR I have heard of has a "native" ISO of 6400. Native ISO is the ISO at which the sensor can produce the best quality image and that is typically around ISO 100. Logically, I think you mean the top ISO was 6400.

If you want to spend the money, the D850 is the top camera today, but you probably do not need its $3,300 worth of gadgetry for what you are doing. If cost is a concern, I would suggest you consider a low shutter count used D800 or factory refurbished D810. The price is considerably lower than a new D850 and it has they have top ISO of around 24,000 if you want to sacrifice a little quality. Practically, they work well to ISO 12,500. Your lens selection sounds good for your needs, so you can save your money there.

chasgroh Loc: Buena Park, CA

...correctamundo! That said, I just sold my D4 and the guy who bought it sent me an email today; he was so happy with the D4 he bought a D5 in the box. Of course, the reason I sold my trusty D4 is I finally figured out that I don't need the D4 as a backup... ;0)

chasgroh Loc: Buena Park, CA

...but, I still own a D800 and see absolutely no reason to upgrade. It is a great body.

jacklewis014

Wished I had been that guy..........

msandersal Loc: Alabama Gulf Coast

I have never looked back since going to the d850, it is a delight to use. It is heavy, especially with the battery grip. Al;so amazing is the DX crop capability where you can see the effect of the FX lens on the DX crop right in your viewfinder when the masking is turned on. A learning curve is there, even for me as a Nikon shooter for years.

mainebrien

I have the D850 and love it. Many expected it to sell for north of $4K, but at $3295, it's hard to turn down. The more you know about its capabilities, the more you appreciate its amazing range of photographic capabilities. It's worth the wait.

SusanFromVermont Loc: Southwest corner of Vermont

Buy the best you can afford! The D850 has lots of great reviews, and the D810 is also a very good camera.

I upgraded from the D7000 to the D810 just before the D850 came out. Since I was still learning to take advantage of the D810's capabilities, it was not practical to jump in for a D850. That said, I am very happy with the D810, it is an excellent camera. And, as OP have said, there are plenty of pre-owned D810's available after all the trade-ins by those jumping to buy the D850. Just consider the advantages/disadvantages of used vs. new such as the warranty length, and difference in price. I bought mine new but in November a couple of years ago with a generous sale price from B&H.

amfoto1 Loc: San Jose, Calif. USA

It really depends upon WHAT you shoot, too.

If you shoot sports, wildlife, etc.... the longest lens you've got is 300mm and a DX camera like the D500 would make that "act like a 450mm" without having to add a teleconverter (and even longer when used with your 1.4X). DX cameras are ideal for long telephoto work, leveraging your lenses to "do more". There can be some significant savings of size, weight and money in lenses, too, if you use big telephotos a lot If you don't need the 10 frames per sec speed and top-of-the-line autofocus system, a D7500 (same 21MP sensor as D500) or even a D7200 (a higher 24MP) might serve very well, too.

But if you primarily shoot landscapes, portraits, macro, architecture.... you'll want wide, and possibly low light capabilities, and more control over depth of field... all of which are better done with an FX camera like the D810 or D850. And since relatively high resolution models like the D850 and D810 can be used in "DX mode", they also might be more versatile. IQ of the DX camera is slightly better than the DX crop from the FX camera. A DX camera may also be faster, smaller, lighter and cost a lot less.

D850.... $3300 body only (FX, 46MP... 7 fps, 153-point AF, DX crop mode = 20MP)
D810.... $2800 body only (FX, 36MP... 5 fps, 51-point AF, DX crop mode = 15.5MP)
D750.... $2000 body only (FX, 24MP... 6.5 fps, 51-point AF, DX crop mode = 10MP)
D500.... $1900 body only (DX, 21MP... 10 fps, 153-point AF)
D7500.. $1150 body only (DX, 21MP... 8 fps, 51-point AF)
D7200.. $800 body only (DX, 24MP... 6 fps, 51-point AF)

Most (all?) of the above are currently being offered with a free vertical battery grip and extra battery.

When it comes to high ISOs and noise, all the above are likely to be able to door better than your older cameras. There has been a lot of improvement in that respect, in recent DLSRs. The FX cameras a whole lot better... the latest DX cameras, not quite as much.

Also be sure your computer system is up to the task of handling 36MP or 46MP image files! That takes a lot of RAM, a fairly fast processor and lots of hard drive storage space! If computer upgrades are needed, that's some additional cost. Bigger, faster memory cards might be another expense, but those are pretty cheap these days.

So, DX cameras can be a bit better choice for some things... FX for others. But, hey, maybe you should get one of each! A D810 and a D7200 aren't a whole lot more expensive than a D850. If you were to consider used or refurbished, you might even be able to buy two cameras for less than the price of the D850.

astacus

D850 in the UK: £3,500.
D3S from mpb : 140K actuations (plenty left!) £790, or wex, 24K actuations, just over £1000

I would seriously consider the D3S, 'old' as it. And, I have a D850. There's something special about the D3S.