You cant change the voltage not without a custom bios anyway, you can change the power limit to 108% which is only a small change but it might help overcloking stability slightly. I can get mine up to 2110mhz, I think I got a bit lucky with that yours might do the same or a bit lower. No you don't void the warranty, not with that card they bundle overclocking software with the card msi afterburner, nor can they even tell you overcloked in the first place. Your fps increase will depend on the game and the rest of your specs nothing to maybe 20-25fps.