I'm an overclocking expert on the Intel Quad-series
The Q67 has a 10X multiplier and the Q84 only has an...8 I think. Same FSB on any board with a 2x difference. Just assume a new 790i with a 1600MHz capability: (1600/4)x10 versus (1600/4)x8
EDIT: Math corrected
Oh, and TD and NE sell them I believe.
TD - Q6700 OEM
NE - Q6600 Retail