e6700 or q6600? or maybe e6850?!

Hey, i currently have a Core2Duo e6700, but am considering upgrading to a q6600, and maybe overclocking slightly to compensate on speed.

On the other hand, as i dont multitask loads, but rather use one or two intensive programs at once (games + itunes + internet for example) i mite go for the e6850 the 3.0 ghz dual core with 1333 mhz bus.

My mobo is the evga 680i SLI...

i am most interested in overclocking potential really, and what kind of 'real life' performance boosts i will see, not necessarily synthetic benchmarks, so loading of windows and in game map load times etc.

Cheers Chris