tbh il be going for the e6600 - which looks like itl have the best multi vs price capability...
for a mach however the sky is often the limit, and more often than not the multi can hold you back....if you have the cash im sure the X would offer better overclocking potential, but imo theres no reason why the 6700 should be clocked just as fast
The £300 odd quid difference is a bit off putting,could spend the spare money elseware,need to find some benchmarks of the 6700 on a mach to make my mind up.