Added a second hard drive.

I recently added a second hard drive on my system. A Western Digital 160 gig at 7200 rpm. My original hard drive is a 60 gig maxtor @ 5200 rpm. I was indeed suprised by how much smoother fs 9 runs on the new drive. In fact, so far all the software I installed on it runs better. I also installed a copy of xp on the new drive as well. Almost like having a second computer in the same tower. Now, is the improved performance mostly do to the higher rpm of the drive or mostly to the fact it's a cleaner disk or possibly both?