the 3.5"/4" PFW pads work well by PC, even on hard clear, but I dunno if they're as aggressive as a 4" SurBuf and I'd suspect not :think: Doing some spot-correction on the M3 with 3.5" PFW/M105/PC took a while.
The Edge/Cyclo brand 4" yellow wool pads can do some aggressive work and are an OK match with M105 (not so good with many other products though).
But this all sounds to me like a case of trying to do rotary work via PC. When you need a rocks-in-a-bottle compound via rotary, then that's simply what you need.
But IMO you can usually get around that by doing *VERY* gentle wetsanding and then using something like M105 via PC.
Hope people contemplating "how do I get more aggressive than SurBufs/M105?" know what they're doing...sounds like a recipe for trouble to me. Getting close to a case of "if you have to ask, you probably shouldn't try it".