Hi again, rupert413!
Truth is, if you are looking at 7,200 RPM drives for upgrading your storage performance, I'd recommend you to use it as an internal HDD instead of via USB 3.0 enclosure. Benchmarking the performance difference and transfer rate of a 5,400 RPM and a 7,200 RPM HDD would be definitely noticeable in an internal (via SATA) environment. However, when used in an external enclosure the drives perform differently due to the USB connection. Even though, a 7,200 RPM HDD would still be faster in terms of transfer rate, the difference won't be so significant really.
Either way, as for the drive inside your WD external enclosure, it may very depending on application. You can check this article from our KB about it as well:
http://products.wdc.com/support/kb.ashx?id=46Anq1
Hope this assists you! Keep us posted!
SuperSoph_WD