The 9600m GT GPU is an improvement over the 8600m GT GPU.
But how much of an improvement? Not enough.
But it's still an improvement. And you can overclock 9600m GT more than 8600m GT. I can run Crysis at 1440x900, med-low (mostly low) settings and get 30+ FPS. That's with the 8600m GT overclocked. If I had 9600m GT, I am very certain I would be able to overclock it and run Crysis at 35-40+ FPS with those same settings, or have it run 1440x900 all med settings at 30+ FPS.
Of course, the newer MBP is better. But in MY opinion, well... I'm not exactly beating myself up for not waiting. If I could do an even swap though, I'd do it in a heartbeat.
I can predict that FC2 will play as smooth as Crysis: Warhead. Should be a small (but MAYBE noticeable) improvement on the newer MBP.