game strutter after OC?

i have 8800 GTS 320Mb stock clock is 513/792 and i Oced to 620/1000. I run benchmark and it work normal, but when i run some of the big game like crysis demo, company of heroes, my game strutter very often. Also, my temp at full load after OC is 75C, is that anything i have to worry about?

 

Temp is fine, sounds like you need to bring down your OC til it quits stuttering