I have a similar setup, Core2Duo E6300 1.83Ghz on an Abit AB9 Pro (965 chipset). I was running the board at 460Mhz, so 3.22Ghz, with the ram on 533fsb (1:1) 920Mhz (667Mhz). Thats about 167%. Then I upgraded the ram to corsair cas4 epp xms2 twinx at £50 a stick. The ram runs happily up to 1200Mhz but required a flash of the bios. The bios flash limited my bus speed to 425Mhz - about 3GHz. So I sent the board to abit for an free upgrade. They decided to replace it and now the bus if free again. However, after breaking the cpu/heatsink thermal compound, I'm running about 10degrees hotter on idle even after renewing the paste. This is limiting me to about 3.2Ghz still. When I get some more I'm sure I will hit at least 3.5Ghz - depending on the mobo and cpu tolerances. Currently, the cpu is at default voltage, but I have maxed out the northbridge 1.45, southbridge 1.7V and memory 2.3V for stability. Only running a 350W psu, and 2x80mm standard case fans.
Not bad for a £20 case, £115 cpu, although the mobo was £105 its rock solid, and passively cooled. (The original 512mb 667Mhz ram which ran at 900Mhz was £26!)