I'd talk to the guys at Red Line, Red Line 20W-50 has an HT/HS of 6.1 and the high film strength of an ester-based oil. It'll stand up to fuel, stand up to the turbo, stand up to the high cylinder pressures and bottom end load. The stuff is a time and a half stronger for HT/HS than most 20W-50 and 15W-50 oils.
They also have a 50 weight (15W-50) racing oil. This stuff is about the only thing I would think of using in that type of application, and I'm surprised you are doing as well as you are with SuperFlo.