Well,
Ive had my 6600 since july of last year, and other than TAT, and a few programs designed specifically to load up the cores, I have yet to do anything that has been able to task the CPU. The things I have done have been amazing. It will rip a CD faster than I could transfer the mp3s from and external drive, it doesnt even notice Norton2005 full system virus scan (it has actually run in the backround during a game without me even noticing it) It flies through renders on 3DSmax and while I have yet to run any of my video editing software, I suspect it process exceptionally fast.
Other than the fact it says zeon, the chip specs out the same in cache, FSB, socket and clock speed. Looks like a higher binned 6600 as MUEngineer said. If you want to OC to the max, spend the extra 10, if not the 6600 will overclock to 3.0GHz on air just fine. I havent even thought about overclocking.
<Edit> If you dont want to overclock, and are thinking about building an entire system, you may want to consider the X26000 @ $229. Its equal to or 1-2% faster overall than the E6600, depending on which review/test/blog you read/beleive.