My Kingcat is holding up pretty good with a 44lb thrust engine on it. But I will say this, there is more movement in the booms when I pick it up after 30 flights with the big engine than there was with 70 flights on the original smaller engine (PST1300R and Titan)
I am almost certain that if I did a snap at full power my Kingcat would explode into more pieces than it's natural original kit form. At full throttle after 3 passes to let the airplane accelerate to the engines full push, I'm doing around 199.250+mph (according to radar), I think a full throw anything would destroy it at those speeds.

Like David says, it is a rugged airplane, mine is a first generation kingcat (when we still had to put the external carbon braces on the booms) but when I fly wide open, I fly smooth and with respect. You push an airplane really hard, you are pushing it's expiration date closer.