Hi Marc, can't answer your question as I have never used a DSLR and long lens. What I can tell you is that the 1000 is capable of producing shots at 3000mm that do not need any cropping, as the birds fill the frame.
I have had mixed results with mine so far, can't seem to get a decent pic in my garden, failed dismally when I first took it out birding, but the last few sessions have produced some (for me) brilliant shots, some of them have even impressed hardened long lens DSLR men
And then of course you have to add in the 4k video and macro down to 5cm or so, and all in all, a superb all round camera.
Birds in flight really don't do it for me, waving a camera about firing off bursts of shots and hoping for 1 good one is not my scene, I prefer to creep about quietly looking in the undergrowth/bushes/trees and spotting and getting a shot at various distances. I also sit and wait a lot
The 1000 can operate at F6.3 at 2000mm very effectively, one of the main reasons I went for it after my 900. There is no doubt at all that the much larger lens lets in more light, so can operate at wider apertures than the 900. Yes it does shut down to F8 at 3000mm, a point that many "professional" reviewers keep stressing, most don't mention the simple "1 click and turn the dial" manual focus, which can be done without taking your eye off the superb EVF.
If your only concern is to get that one extra special super sharp image then stick with a DSLR and separate lenses, they can look very impressive when walking about or resting on a bean bag in a hide, and to be honest, had I lots of cash to spare I may well have gone down that route myself some years ago, but having purchased a Sony FD185 (the first digital camera) with a 10x zoom I was hooked. I then went to video cameras due to the long zooms of 20X and then 30X and extracting stills from the video, then stuck an 80mm scope on the front.
When the Nikon 8800 came out I went for it and was well happy used it for a few years and sold it to help buy the 900 (which I still have) but when the 1000 came on the market I dug a bit deep and took the plunge, £1000 is a lot of money to me, but money well spent.
Sorry to go on a bit, really what I am trying to say is that "getting the shot" is more important than worrying technical issues, and the 1000 will get the shot in almost any situation you are likely to come across.
I only view my pics on a computer screen, albeit a very good screen, or pics for the album at 6"X 4" so even a just reasonable shot will be good enough. I don't pixel peep, or at least didn't until now
now I am getting a bit obsessed with feather detail...……………...
Den