Re: E6550 vs E6600
Right off the bat (I don't have any experience with this CPU), the faster bus should make it a better CPU compared to the E6600. Plus, the E6550 has a higher temp threshold at 72 degrees Celsius compared to the 60 some odd degrees of the E6600, which tells you that you can OC this baby more comforably than the E6600 can. So I guess it can be faster than the E6600. Otherwise, they're nearly identical. But the faster CPU bus should be beneficial.
The E6550 and E6600 OC'd would perform about the same despite the higher FSB of the E6550. Both CPUs have the same amount of L2 cache, 4MB. The E6400 and E4300 OC'd to 2.8Ghz will also perform about the same since they also have the same amount of L2 cache, 2MB.
I'd get the E6550 since it's cheaper than the E6600 yet performs pretty close to it at stock speeds.
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?