I used to run a 46fx + tower muffler on 10% nitro, now I have upgraded to YS 63S, the YS runs really great and getting stronger every run, never deadstick but until now I have not noticed a large diference in thrust, Maybe the history of ex pylon racer of the Fx makes it stronger, the main reason to go for the 4 stroke besides the larger torque on the low end is reliability; the fear of a deadstick on low 3D maneuvers now it`s gone .
So, a good running 46fx (AX and maybe 15%nitro would be better) it is not a bad thing, but it is a must to be extremely carefull on carburation mainly the low end needle.

Daniel