66 and 133 refer to the peak transfer rate in MB/s the hdd can in theory achieve from or to the hdd's cache. This is only a brief burst and in fact is never achieved in practise. The drive's normal transfer rate when reading from or writing to the disk is much slower and well below 66MB/s. You will notice very little or no difference with or without the add-on card so save your money. If you don't have much RAM use the money to buy some more, the benefits will be much more apparent.