Here's the result of the old baffle piston .61 and an APC 11x7. I don't know how close the load is between an 11x7 and 12x6 APC, but it seemed to like the 11x7 better. It peaked out at 11,760.
Bill, thanks for the info. My prop drive washer is machined and will not pull off by hand. My engine must be the 6550. Does anyone know what horsepower it takes to turn an 11x7 @ 11,760? Is altitude considered when computing horsepower?