I don't think HDs matter when it comes to o/c'ing. Unless you have a SCSI adapter, PCI IDE/RAID controller, or a bad chipset "cough" i820 *cough*, then you don't want to push the PCI clock too high.
There are good performing hard drives though. Quantum Fireball Plus AS, IBM Deskstar 75GXP, Seagate Cheetah X15...mmm! Can't wait to see what the IBM 60GXP has in store!