About the overspeed issue... the manual assumes you'll be one of those guys that puts the plane on the runway, advances the throttle to full power, then leaves it there until it's time to land. Those guys aren't going to be hovering, so they don't need any more power than the 46. The 46 would be marginal for hovering even at sea level. With a Nelson muffler or mousse can a 46 would still be on the weaker side. At 5000 feet, you want something bigger. Don't worry about overspeeding, you have a throttle to take care of that (don't tell the full throttle guys, they won't believe you anyway)