Speeds of ram for HP laptop...PC5300 0r PC6400?

[MiG29TangentBoy]

My wife is getting her laptop replaced by Best Buy, and I'll be kicking up the memory to the 4GB max as soon as we get it (Pavilion dv9608nr). But Crucial's site lists PC5300 and PC6400 as being compatible...is there any point to getting the faster ram? Or is it a waste of time? (And why the heck is there a PC5300 and PC5400? Splitting hairs, are we...?)