I've been using 6" pads on my PC, and have been happy with them, I just got in my 7.5" pads but haven't had a chance to try them yet so the jury is still out on them.
I have to agree with the Fuzz. I like the 7.5 inch pads. The backing pad is much sturdier. I use them on the PC as well as a rotary. They seem to do the job very well with both.