I think that xbx2 is not really made for quad (not extreme) because the fsb max is too low.
But, with extreme quad, like my tests show us, it is nice, with acceptable t° and no high voltage.

So, i can boot @380 and more, but not stable with stress software like Occt and csmt (cpuStressMT).

I never obtain stability with q6600 and fsb more than 346, although i set vMCH to 1,7, vFSB to 1,65 and of course some vcore.

My tests are over with this motherboard, i keep it with my qx6700 @ 3420 (12x285, best freq for DDR2) or 13x266, and less temperature and vcore.