noob ram question

I plan on overclocking my Q6600 once my new case/psu/mobo arrive. My motherboard is the GIGABYTE GA-EP45-UD3R.

I currently have 8GB of corsair 800mhz ram
I have access to 8gm of 1066 ram. (I'm vista 64 bit)

My buddy says he under-clocks his ram. If that's the case am I fine w/the 800mhz ram or would i be better off going for the1066?

You should be fine with the DDR2-800 since a 400x9 OC would be 3.6GHz on that Q6600.