I replaced my PS2 40GB 5400RPM hard disk with a 7200RPM one and that is a touch quicker as well, so worth the few quid over the 5400 ones.
Any noticeable disk noise? The thing I like about the HDD my PS3 came with is that you simply don't hear it. My notebook's 160GB WD drive, by comparison, is a horribly clicky-clacky drive, and it's only a 5,400RPM.