I can't tell you too much about firing 12s & 16s without recoil pads. I'm 6'3", 200 LBs and formerly thin. Over the last number of years, since being infected with the SxS disease, I've had my gunsmith install recoil pads and sometimes spacers to increase LOP on about a dozen of my guns.
However, I can tell you about pitch. Even with Pachmayr Decelerator pads installed, in several cases the pitch was all wrong and I FELT IT IMMEDIATELY. I have a somewhat "bent forward from the waist" style of shooting and now know FOR ME I prefer very little pitch on my guns.
