Well the main reason people are commenting about it is because a 4870X2 at that res is quite useless since it does very little work.
try it at 1920x1080p and see if it runs that great.
As for the FPS boost, I have heard that 7 is highly optimized. I only wounder if they will give Vista the same optimizations via SP2....
will try it at 1080p
oh and i bloody hope so about sp2 would be great!