Just flew my Widebody for the first time tonight- O.S. .91 FX with Std Muffler W/ Baffle, silicone exaust deflector, 2.25 Truturn and an APC 15x7. Seemed the perfect combo of thrust and speed, and didn't over rev. also the 16 oz. tank gave some long flights. I would stay with the 15x6 or 15x7 for the .91 Fx. My Dad runs a .91 Fx on his goldberg Extra with a bisson pitts muffler and an APC 15x6- little louder than mine, but pulls great all the same. We both have tanks right behind the firewall and are running stock carbs without pumps.