I’m running an APC 18x8 wide prop and getting 7800 rpm. I’m using the stock Walbro 11.11mm carb and the stock chainsaw muffler. I think I could get even more power by opening up the exhaust and going with a larger carb, but I’ve already got unlimited vertical on my 14 pound stick plane and it is very quiet. I’ve ordered a Menz S 20x7 that will hopefully be in this week that I’ll try as well.