Well, the Sea Duck has a 56" wingspan, and is top wing; a great FT plane, flies like a trainer and is super solid. I've built my second one just recently (the first one, several of the glue joints finally gave up and came loose after almost 2 years). The only downside with it is the wing is glued on and not detachable.
There's also the A-10, another twin engine plane; that one has a 60" wingspan and a detachable wing, but it's a low wing plane, not a high wing. However, it has a lot of trainer-like tendencies, so you might not have an issue with it!