With the keyboard, I don't think it really matters if it is USB or PS/2.
With the mouse, it used to be the case that PS/2 had a lower sampling rate compared with USB mice when using older versions of Windows (you can use some third party programs such as PS/2 rate to increase this). However with the newer operating systems, the sampling rate can be increased up to 200 reports/sec.
I hope this info is accurate