I bought this device to replace an older HP external drive. This WD drive comes with a USB 3C cable and a USB 3 adapter. Im using it on a MPB - USB3 port. WD will only give me "theoretical" speed and not practical speed or expected speed. Can anyone comment on what I might expect? I seem to only be getting 46 to 61 MBps transfer speed which is slower than the 7 year old drive its replacing. Trying to figure out why. Tks for any help!!