Currently I am on:
Intel G965RYCK mobo(doesnt support C2Q BTW)
1 Gb 800 mhz ram
Acer 22" 1680X1050
Well, firstly I am satisfied with my current config. I have around 200$ to spare. Is there anything that I can upgrade in here and expect a 10%(atleast) rise in FPS? Games I currently play run fine(except gta4 BAH), and no new games till december(when blizzard explodes). So what can I do with that cash? CPU upgrade will give me more than 10% gains? Or shall I wait and do a system rehaul?
Get a GTX 260 for ~$180. You would see more than 30% gains in every game. Although your CPU can be a bottleneck, so you should overclock it after buying an after market cooler for the rest of the money.