I am using this computer for mostly gaming. with my ATI 6870. However currently i have an AMD phenom II x4 810 cpu which runs at 2.6ghz. For some reason my motherboard bios will not let me overclock. I am curious to know if there would be a huge difference if i switched to a AMD phenom II x4 960T 3.0ghz cpu? If it raises my FPS by like 10 then i will buy it. I currently have this motherboard.
You won't be able to overclock by raising the multiplier unless you have a Black edition CPU, so you have to raise the base clock (not sure what it is called exactly). It is very unlikely that the other CPU you mention could increase your framerate by that much – not to mention that you can probably overclock to a similar speed.
Yes, you can overclock your current Phenom II by raising the HT reference clock. The HT Ref Clock by default is set to 200 Mhz. The multiplier for your CPU is 13x. If you were to bump your HT Ref Clock to 233, the processor will run at 3 Ghz. This will mean, of course, that you will have to OC your memory as well, since it's speed is also controlled by the HT Ref Clock. DDR2 actually has some decent overhead that you may not have to bump the voltage any.
The good news is that the Zosma (960T) should run fine on your mainboard. Make sure you have the most recent BIOS update available. The Zosma multiplier is unlocked, so any overclocking should be a matter of turning up the multiplier and testing for stability.