The 15/16 MC gives slightly less pedal effort. The original manual disc MC had a 1-1/32 bore, and made for a very stiff pedal. People who are used to power brakes tend to think it's broken...
Great thread, BTW.
I recommend the Summit slotted cross-drilled slotted rotors for pretty much the same money (I think they were $80/pair), made in USA. I am also using Summit's ceramic brake pads, and they survived the Willow Springs road course test -- they really bite, and do not fade.
The K-H brake setup is a solid design (4 piston fixed caliper with vented disc -- that spec sounds more like a Porsche than a Plymouth), and now that parts are getting more available, I don't see any downside. People used to complain the pistons would freeze up, but those were 30 year old seals. If you use them regularly, I don't see a lot of problems.
