I don't know where you're getting your info (and I haven't personally looked), but the 7600 should have more hardware than the X1600... remember its the mobile version of the X1600.
Regardless, the real question is whether the 7600 will give you enough performance to run at 1920x1200 vs the X1600 at 1680x1050. Unfortunately I don't know the answer, but it would be interesting to know. What I do know is that the 7600 is significantly faster than the X1600, so my guess is 'Yes'. As to whether you will get more frames from the 7600 at a higher resolution, I would have to say No.