Confused about external hard drive speeds

I am looking a purchasing an external portable hard drive for LR4 (personal use only) to use with laptop and desktop computer.  USB 3.0 may be used.  I see that there are two options available regarding rpm 7200 and 5400.  I have been told that 5400 is as fast as the USB 3.0 port will allow so 7200 rpm is not going to speed things up.  Is this the case?

Also looking for thoughts on LaCie Rugged external drive and ADATA brand drives.  Thanks.