I've tried the 75cc kit, the 15/15 carb and the Pollini pipe and the piece of equipment that made the most difference in all around performance was the kit. if you are afraid to take the cylinder off stick with the carb and pipe combo, it's surefire. but personally I'd just get the kit and try to be responsible about riding. break the rings in for 300 miles and ALWAYS let the engine warm up before giving it full throttle.
with these mods + 11 teeth in the front and 28 in the back I'd hit at least 45 on the flats and never had a problem with tires/brakes or the frame.
the acceleration wasn't bad either.
daveb