All else equal, is a larger MB550 more stable than a smaller MB450? Does a 550 offer a larger "catch area" than a 450? Thinking of trying a few MB550s out next year...

Yes,they have an inch more holding power.I haven't used the 450's but all coil spring traps I've used need some bedding technique.I haven't found one trap much easier to bed than another,for me at least.Good traps though.

It may just be me but I’ve found it easier to bed a smaller trap more solidly than a larger trap. Having said that, the mb 550 beds very well. Personally I’m considering a switch to longsprings for land trapping. Solid bedding is one reason.

I have some of each, I love the 450 for fox, and the 550 is my go to coyote trap, I try to avoid using them if I know fox are in
the area, then I just set my 450`s.

Never had a pullout out of either on so far.

Practice bedding whichever traps you use and get it down to perfection. Each brand may be a little different in how they sit in the bed. Practice until you can reach blindly into a tote full of different brands of traps and then bed the one you grabbed. You do this and it won't natter which one you grab. I am known for just mixing mine up and not sorting them by brands when I hit the lime to start setting. All are mostly #2 coil spring size traps, 1.75 Victors, MB 450 and 550's, Montgomery #2's, sleepy creek #3's Tons of fully modified Bridger 1.65's, Bridger #2&3 dog on and dog less and lastly the Montana #3 dog less.

Master the art of proper trap bedding regardless of the brand of trap, you can do it with some practice and then don't worry about brand of trap, just make sure pan tension is good, springs are in good shape and slam the steel in the-ground. Practice breeds competence, competence brings success . Success fills your fur shed. Get the most basic part down to perfection and the rest will fall into place.