Good advice. That is why I am keeping all the Nikon gear for now. I shoot a lot of wildlife and am interested in how the A9 will preform with the 200-600 as compared to my current Nikon D850, D500 and the Nikon 200-500 and Nikon 500 5.6. I will be shooting each extensively this winter in Florida.
I plan to shoot a different one each day in the same environment.
One of the big advantages of mirrorless is the fact you do not have to fine tune a lens. Many experts on Nikon and Nikon itself caution fine tuning a lens on a DSLR. Why? Because, contrary to others OPINIONS, these experts on Nikon say you can only fine turn for one distance, the distance you fine turn the lens for. Others will argue that once a lens is fine tuned, it is fine tuned for all distances. Physics just disproves that rumor all together.
Anyway, all the arguments become null and void with mirrorless. No longer will one have to fine tune. I shoot wide open to blur the background on my wildlife shots, so I am anxious to see the results from the mirrorless A9.
I am also interested to see how the metering systems compare.
Like I have stated before, I have had Sony mirrorless before and used both systems together. So, I will be doing so again. I would not be surprised if I do not end up using both systems together again.
Using each what each excels at.
Anyway, I tend to go on and on. But, I will be posting comparison's this coming winter. I will probably start posting in January some of the primary results and observations about the comparison's between the mirrorless and DSLR.
Thanks for your post. And keep on shooting until the end.

I am going to get started on mirrorless AGAIN. Just purchased a used, under 4000 clicks, Sony A9 with grip for around 2 bills. I think I am going to match that with the new Sony 200-600 and compare that to my D850 with the 200-500. If the results are favorable I will start the slow transition to Mirrorless.
After much contemplation, I believe Sony's focusing system is that much better than Nikon's especially in mirrorless.
So, I will go one step at a time and continue to compare results. And I will share them here. If the results are good, I may add the 400 2.8 or the new 600 4.
OK, I am also looking for a general purpose G lens. Open for suggestions.

Yes, I had the EVF on my Sony A99 and A77II. I shoot a lot in manual and you can see the exposure change as you adjust your settings right in the viewfinder. I shoot a lot of shots at sunrise and sunset using this feature. In fact, I will look for one of those shots. I was deliberately underexposed for effect. Let me see if I can find it.
OK, I actually found it. It is a image of my son and his wife taken at sunset at Cap Cod. Anyway, it would have taken a few minutes to get the exposure right in a DSLR, but I set it up quick with the Sony A77II because I could dial in the sky and get the silhouette I was looking for and at a fast shutter speed to capture the jump.
So, yes, one of the big advantages in mirrorless is seeing the exact exposure in the EVF before you trip the trigger.
And, yes, I know, the horizon is not level. This was the image before PP.

I am going to get started on mirrorless AGAIN. Just purchased a used, under 4000 clicks, Sony A9 with grip for around 2 bills. I think I am going to match that with the new Sony 200-600 and compare that to my D850 with the 200-500. If the results are favorable I will start the slow transition to Mirrorless.
After much contemplation, I believe Sony's focusing system is that much better than Nikon's especially in mirrorless.
So, I will go one step at a time and continue to compare results. And I will share them here. If the results are good, I may add the 400 2.8 or the new 600 4.
OK, I am also looking for a general purpose G lens. Open for suggestions.