over Clock help

Need Help over clocking my water-cooled system RIG the Goods : (D975BX2)Bad axe2 motherBoard  RAM(in bios says default 667-factory says 800)gskill Dual cannel DDR2 x4 GB ,Q6700 quad core  2.66, Ati 2600xt,koolance custom water cool setup runns very cool,Sata  hard-drives 3,leopard 10.5.7,not sure of the bios version,but I did notice it tends to lockup on me when I try to  bump up the 10x multiplier in performance  menu for the  CPU...my goal is to get a stable system tweaked to around 3.6-4.0 MHz with my rig...I hear the memory and cpu tweaks is the  key to getting a system in Harmony,thanks Insain this is a great community...