The RPM of the drive,does not translate directly into a linear measure of actual read or write results from the drives. This also depends on platter size, medium of transfer etc. For instance for 500GB 2.5" drives, there are 5400 rpm drives that are pretty damn fast compared to any other 500Gb drive.
I would look carefully at the reviews of each drive to understand what real life performance you will get. Storagereview.com, Andandtech.com are a couple of places to get hard measurements from comparative tests of the different drives.