Re: 3" pad on porter cable
Yes you can use a 3" plate on a PCxp, no problem. I have that with the Optimum Micro fiber 3.25" pads, works great!
Don't forget the plastic washer, and also keep in mind smaller pads cut a LOT faster than bigger pads, but 100% concentration is important...
Also, it's a lot easier to tip over the polisher and scratch the paint, another reason to pay attention.