Mabey go for an i5 750? from the few reviews ive seen thats got the i5 750, i7 860 and i7 870 all tested on the 100% same set up the 750 was on par if not better than both the 8xx's clock wise and for £50 cheaper its what id get, unless you need the virtualisation and hyper threading of course get an 8xx.
The i5 670 is a little beasty aswell if you dont mind a dualy, belgiums OC team managed 5.4 on air @ 1.55v and theres a few other people that have managed 4.8-5 on 1.45-1.5v, IF i remember my facts right the max recomended for it is 1.55v acording to one of intels data sheets off there website aswell so its not like there suicide run volts.
TBH it depends what you want out of it.