OCC informed me that they have published a major update to their Intel Core2 Q6600 CPU review adding the E6400 and E6600 to the testing. Here's a taster:

From all the above results, the only reason to buy the Q6600 over the E6600 would be if you do a LOT of encoding, rendering etc etc. The performance boosts for compression/decompression, and encoding is unsurpassed. However, if you're a casual gamer looking to build a new gaming rig, then I'd have to recommend the E6600. Currently, there are simply too few games that fully take advantage of SMP. Even in games that fully support SMP (Rainbow 6: Vegas), you'll only see improvements of 10-15 fps, which in my mind, isn't worth the extra cost of a quad core chip. Thankfully, with the ability to overclock these processors so easily, you will be able to milk every last drop of performance from them. The raw power that these new CPU's have to offer makes them the current crème de la crème. I would say my major concern about this processor would be the highly inaccurate temperature reporting that this CPU has.

After looking over the benchmarks, it's hard to pick a clear cut winner; but in price vs performance you definitely have to look strongly at the E6600. With overclocking, these CPU's have the ability to reach 4ghz and that makes them much more appealing for the price. In the gaming benchmarks, you can see just how well the E6400 and E6600 do against the quad. Now if you have the need for major multi tasking, then the quad is probably a better option. We will be adding more CPU's to our benchmarking list as the weeks go buy so keep checking back often to see how the rest stack up against the quad.