We use HIPS 8 in a predominently VDI environment and I've not noticed any issues at all. At present I'm logging only and seeing very little come back for VDI clients. We don't see any performance issues specifically relating to HIPS either.
Given what is being reported for High and Medium signature triggers I'd have no hesitation in actually turning HIPS 'on'.
If only I could turn the noise down coming from SQL I'd be turning it on for servers too (again many are virtual) but its going to be a long process to sift through them until we're ready to turn it on properly.