bgmartin,
I would get the WD. I've seen a couple of different reviews in which the performance of both drives is better than most competing drives. (If I remember correctly, the IBM is better at some things, the WD at others.) However, due to the extremely high failure rate of the 75 GXP drives and many reported problems with the 60 GXP, I would avoid IBM. I currently have two 75GXPs and I've all ready RMAed one.