WD has two entirely separate line of Hard Drives, their mainstream 5K RPM and their performance oriented 7K RPM drives. Their two totally diffferent faimilies of Hard Drives, and are not comparable.
Their 7K line is available in capacities of 20GB,20GB,40GB,60GB,80GB,100GB, 100GB "Special Edition", and 120GB.
Their 5K line is available in capacities of 20GB,30GB,40GB,60GB,80GB.