Port, you might want to also try APC's 12.25x3.75 prop. Everyone that has mentioned using this prop with a .40-.46 has reported the best overall thrust.

Hobby, I was going to say that the stab might have weakened from cutting the covering for glueing it to the fuse, but looking again at where it broke, looks like that's not the case. IMO, the UCD's stab just isn't very strong but when reinforced, will take all the punishment you can throw at it.