It shouldn't be. How are you temperatures on your GPU when you game out?
As long as your card isn't getting too hot (over 75C) you should be good.
Edit: Also it's a good idea that you have a strong enough PSU to handle the overclocks of your GPU. What are your complete system specifications including power supply?
Hmm, my card is an ATI Radeon HD 4350
Intel Core 2 Duo E7200 @ 2.53 GHZ
lol, it gets to 85 FPS when OC'd and Gaming