If it is the red Jett muffler it wants to turn above 15,000 on the ground. That will get it into it's sweet spot in the air. I used to run a 9x8 on my TT 46 Pro with an Ultra thrust. It was about the same load on the engine as the 10x6. It really depended on the day which was faster on the course. The 9x8 had a little more speed but the 10x6 lost less in the turns. Either would break out in bronze if I flew a tight course. My son won a few trophies with that Strega.

Blessings, Terry