I have no doubts, a buddy of mine has a 55 AX with a Jett muffler and power was very good until it needed new bearings after a year. There however is much more to engine performance then just the numbers on your tach. Think about it for a minute, in 1985 a SF .46 cost around 130.00. Today a .46 AX cost about 145.00. Fewer engines are sold now compared to 1985. Modern manufacturing techniques will account for some cost cuts as will moving manufacturing to china but engine prices are pretty close to the same while just about everything else has tripled in cost.