I've got the PC pipe & muffler on my bike, I preferred it over the torque pipe (but am aiming to compare the two again soon).
I was worried it would make the bike more like my YZ80 (peaky), but actually liked how it delivered the power. I seem to have a different perspective of the KDX than a number of people here & that I've spoken to, as I've found the power very friendly and to me it doesn't have a "hit", it just pulls strongly. The torque pipe delivery seemed a bit flat. If I had to buy again, I'd probably go with the PC. But again, it depends on your riding style and preference. I haven't tried a rev pipe (can't justify another one), so can't compare to that.
I ride single track, sand based forest most of the time, and am as slow as a wet rag.
Michelle