The thing I have noticed is some mobo's can be stable with a dual at 400 + but if you switch in a known 3.6Ghz Q6600 it may still have trouble with it. All depends on the mobo... but yes not all but damn near all. It really does take a while to figure out the magic pill and in some cases... for stability its better to run it at 3.2Ghz than 3.6...
Better to have near 100% stability versus 80% at a higher clock...