Hi, to overclock a Core2Quad, you need not only a good cooling but a good motherboard and power supply as well.
For motherboard, and in term of overclocking, I would highly recommend you either Gigabyte or Asus with P35 chipset and with at least 6-phase power. Nvidia 650i is highly NOT recommended for overclocking a Core2Quad.. Between all three motherboard of your choice, I would recommend you Gigabyte P35-DS3, although if you can afford P35-DS3R (should be slightly expensive), that would be a slightly better motherboard in terms of overclocking
If you're planned to do SLi I would recommend you Abit Fatal1ty FP-IN9 SLI for the similar range price with P35-DS3.
I'm in Malaysia, thus I don't have a clear idea about motherboard pricing at your country.
And you might want to consider a good and reputable power supply for your overclocking needs. A 500watt ++ with at least 36A on combined +12v rails (or 18A for each +12v rail) is highly recommended.
Thermalright 120Ultra Extreme is excellent choice for overclocking. Or you might want to consider either Xigmatek S-1283, CoolerMaster GeminII (Does not come with fan) or Thermaltake Big Typhoon VX for great budget cooling