I'm no expert (I always start a post where I'm disagreeing with the consensus that way) but I really see no reason not to use the .46 if you've got it, especially if money's tight. I built my LT-25 with a Fox .40BB on it, and it has no negative flying characteristics that I can determine resulting from this engine choice. It does climb like a ROCKET, though! 1/2 throttle is all that's needed for takeoff. Mine balances without adding any unneeded ballast, and really, the LT-25 has similar wing area to most .40 size trainers at slightly less weight. It can also still slow to a crawl and just lope around the sky in a trainer-like fashion.