Here's my situation, I have a 150GB Raptor X for my main hard drive (almost full), I have a second drive, a 320GB WD I use for backup. Basically, I just clone my 150 to the 320 every week. I want to sell the raptor x and the 320 and get two 640GB WDs. Will there be any sort of performance gain/loss between a raptor 150 and a 640WD?