I think 42 is too high. I'm guessing the manufacturer is covering its ass in the event of a blowout due to high, sustained speeds, in hot weather. If you ride like that, then 42 is good. Otherwise, at 42 there is less rubber contacting the road and therefore less grip for braking and cornering, not to mention a stiffer ride. I don't go above 36 and I'm 215 lbs. However, too low and you will wallow in high speed turns. So it really depends on your weight, whether you have a passenger, and how you ride.