Haha actually i moved from a d300s to d7k. I had a d90 then went for a d300s because i loved the feel of the camera. But i in the end went back for a d7k (didnt lose money in swopping d300s for d7k) because i did not need the speed of the camera. And although people might say that the imagine quality does not really matter, it matters quite alot to me.
The d300s was only usable pass iso1600 which really threw me off it. I understand how a 24-70 feels on a d300s, it feels made for it but when i use a 24-70 on a d7k with battery grip its equally nice to use yup. I also felt that sd cards were much more convenient for me to use, and nowadays high speed sd cards make the gap between CF and SD not that big anymore. I just love the convenience of the SD card fitting into my laptop. And yes to the 51 Af, that was pretty shiok to use however i found the jump from 39 AF pts to 51 pts not as great as the jump from 11 to 39 pts from a d90.
The thing is the d90 when u tracking an object if it lies in between the points u will find that the camera gets confused sometimes. Thats why i found 39 af pts onwards to be useful because the graduation between each point was much smaller. But at the end of the day i would advise getting a cheaper body and at least a 17-55 f2.8 for dx bodies if not the 24-70. No point having a good body with lousy lens. You are better off with a d90 and decent lens