My 40FP turns an APC 11x4 at 12,500 with an open exhaust. I can't find my data sheet right now, but I'm thinking with a 1.75"x6.5" can, and a 1/4" outlet hole it turned a shade over 13,000. I would think your 40FP with an 11x3 would turn even faster.

When I tried the 1.5"x5.5" can on the 40FP, I got similar RPMs, but the needle valve setting was really sensitive, and the throttle response was really screwed up.

If your 1.75"x6.5" can didn't work great, check to make sure the outlet hole isn't partialy blocked with JB Weld. This would explain having to lean out the engine so much, and the lack of RPM gain.

I also agree with bbjoe about having low end and mid range running problems with the A3 plug. The OS #8 cured that completely.