Damn, Rich, you're already in the clouds! We are at about 1205' here. Plenty of air.
I couldn't agree more-I don't like underpowered aircraft either. In your situation I think larger engines would probably be warranted. You just have to allow for prop clearance before installing the nacelles. I moved mine farther apart just in case. I am running 9 x5's now and have about an inch of clearance between props. As it is, I think I'll stick with what I have on. As good as it's flying with them, and turning about 15k, I ain't going to fix it if it ain't broke, as the saying goes.
I'm assuming you have the 80" Bronco, based on weight and engines. I'm presently working on the small version. It's quite a build.
Good luck on the plane and keep us posted on progress.
Randy