I'd go with the 55 AX, and drive the airplane instead of going full throttle all the time. If your Seagull PC 9 is anything like mine was, it will handle it and handle it well. You don't have to fly at full throttle unless you're only interested in speed. The 55 AX should be awesome on the up lines!!

"Experience is a hard teacher. She always gives the test first, and the lesson some time later!"