As of right now, very few, if any games take advantage of 4 cores so the E6850 is the clear winner. That will most likely change in the next few years as more companies program their games for multi-threads.
My son has a Q6600 @ 3.6 and I have an E6850 @ 3.6. In Crysis, our FPS are nearly identical. At stock, the E6850 would be the clear winner. His setup requires an aftermarket cooler, whereas mine is nice and cool with stock cooling.
If you just go by benchmarks then yes, the quad is the clear winner, but 3DMark is optimized for quads and games are not YET. I score over 14,000 3Dmark06 and he scores over 17,000. At stock they both get around 12,000 range, with the quad slightly edging me out.