|I'm curious if you had the E6600 overclocked? It would have easily done 3.0GHz.|
According to the JEDEC standard, all DDR2 memory is supposed to run at it's default speed at 1.8v. The fact that your RAM requires 2.2v should have tipped you off that something's not right. Why would DDR2-1066, which should run at 533MHz at 1.8v, require 2.2v?
Since you switched to the 1333MHz FSB CPU, did you underclock your RAM to 333MHz speed to match the CPU frequency (1:1 ratio)? Or are you running it out of sync at 533MHz (5:8 ratio)?
"I have read that XP and other OS's have required full reinstall of OS"
If all you did was change the CPU, you do NOT have to reinstall the OS. I don't know where you read that, but I suggest you stop taking any advice from that site.
BTW, 5GHz is unrealistic. Did you get that info from the same site?