I'm going to replace my iMac 24" Alu WD HDD today & going from 320Gb to a spare 1Tb drive. I think the replacement drive will be a 5700/ 5900rpm drive SATA II. Will this be ok as I read that people recomend a 7200rpm speed drive to be used with the iMac. I think I will be fine but I thought this may be for optimisation? Can anyone help before I take the plunge?