U can overclock to ~3.8 GHz or so with your mobo and aftermarket cooler easy.
The Intel i7-920 can be overclocked and you would have to go into the motherboards bios to see the options for overclocking that cpu , what you want to look for is the cpu multiplier and at stock it should be running at x25. That is what you first want to use for starting to overclock and you can increase that multiplier untill windows becomes unstable at which point you would decide to stop and back off 10% or start adding voltage to make the overclock stable. I know by just reading this that it sounds easy but this is just a quick condsnsed version so you get the idea and there are stickey notes at the top of this forum that have more info into doing the overclocking process. The one thing that you are going to need is patience , because it is actually a very tedious process and with each increase you have to verify that the increase is stable so it's a lot of going into the bios and then into windows for testing and then back to the bios and then back to Windows for testing. So when you decide to do the overclock plan on it taking a few hours. The end result is worth the time invested in a stable overclock.