you may, but it won't be earth shattering since you are already raid. But take a look at Tom's hardware charts, they test hard drives and you can look at how they compare at various tests:
Would the 640 drive be roughly the same as the 750 listed on toms. The only diferrence in the part number is the 640 versus 750.
Edited by Tufelhunden - 6/15/08 at 7:55pm