Whenever I am capped at 90 fps (nice job infinity ward, your games are getting worse as time goes on) or below everything gets all skippy and stuff. Playing MW3 or any COD at the default fps is messed up. On all of the other cods I will max myself at 125 250 or 333. However infinity ward thought that MW2 wasn't bad enough so they had to make something 100% sh*t, MW3. Seeing that MW3 is capped at 90fps the game feels like a slideshow, I'm already dealing with motion sickness due to a 65degree FOV.
ASUS M4N68T M V2
AMD 965 BE @ stock
GTX 460 1gb @ stock
4gb ddr3 @ 1333(I think, I know I'm at stock though)
Drivers are fully up to date
Temps are fine GPU at 32c max CPU at 57c max
I am using fraps and I'm running a constant 91fps, never seen it go below.
Unless you have a monitor with 120hz, after 60hz, it shouldn't make any visible difference other than you'll get more screen tearing. Motion sickness issues shouldn't change after 60 FPS for the same reasons.
However, I also have motion sickness issues, and I can tell a difference up to 75hz, but my monitor does display 120hz.
Although, one theory to this simulator sickness is it's caused by latency and there may still be latency issues beyond the refresh rate of your monitor.
I'm not sure what would cause choppy looking game play if you are already at your monitors refresh rate or above.