I use the same board.  I run my Q6600 G0 at 333 FSB.  At this speed, instead of the stock 266, I simply set my ram to the option of PC800 within the BIOS with no need to OC it.  However I have tried oc'ing the RAM and have had success with my 2 brands. I have 4 sticks (1024) of Patriot PC2-6400 4-4-4-12 2.1V and 4 sticks of Crucial Ballistic PC2-6400 4-4-4-12 2.1V.  I have tried both sets and I can get both sets to run at 500mhz (instead of rated 400mhz) by loosening the timings to 5-5-5-15 and running 2.1-2.2 V on that same board.
Good luck.