[slotloco]

Just thinking about the comparative performance difference between G25 (shore 25?) and the magical NSR tyres in the original posting, is it simply the case that softer rubber grips better than harder rubber? So SI G25 is harder than SI F22, which in turn is harder than NSR Ultra15...or are NSR tyres made out of different stuff?

I think that is a big part of it. You only have to feel the difference between Hi-Grip medium and Hi-grip soft, or N18 vs N22 when you need more grip.