i just got a hell of a deal on the 421 cheeta, that is why i am going with it, i already have the carbs and pipes, but we trail ride about 20 miles each time we go out and hill climb (coal hills), i ran cpi's and shearers before and i did not like them for trail riding, i know the cheeta is alot more top end so i figured that i would run the pro curcuits to gain a little more bottom