I've built it with stock dihedral and flat, and am just now building it with about 2 degrees.

Just so you know, the flat wing will be more agile that the stock dihedral, but on the ground you will take a lot of ribbing because of the 'droopy' wing. It just looks that way.

By the way, when I built it flat, I bought new balsa and ran the center section sheeting all the way across. I think it made it stronger.

The flat wing will fly inverted more easily and will roll much better. The changes won't be extreme or dramatic, but they'll be there..

Right now, I'm building a new one with about half the dihedral in it. Just something to bore holes in the sky with.. it'll be fun whichever way you make the wing..

You might also consider putting in two ailerons and running flaperons. Just remember that those wings have to be super straight and the flaperons have to drop evenly. Try them out one mistake high, straight and level, the first time if you go that route.

Enjoy...

Just my $.02

Bob