My upper of choice on the three PCC's I've built has been the Aero Slick Side. No need for the FA so why have it? Makes for a very clean looking rifle. As for comps, I've used the JP on two and an Armalite comp on the third. I opened the comp up to 9MM, sent it and the barrel to ADCO and had them cut and re-thread it so the barrel would be just over 16" pin and welded. It came out pretty nice.