^^I think there is only one G31 board from gigabyte, and it does overclock well. Around 2.4k for it
But the problem is the CPU has only 1 mb cache, its gonna be a bottleneck at whatever speed you run it at. If you have the cash would suggest a CPU upgrade too
Cheapest graphics card is either Geforce 9600 GT for 4.7k or Radeon 4670 for 4.4k
4 gb ram will not make significant difference right now but to be future proof it might not be a bad idea