The difference, ignoring dihedral and airfoil configuration, is that the CG is moved closer to the middle of the wing. With the same airfoil and wing configuration, that just means the low wing plane will be more agile. You could also phrase it "more unstable", which is necessary to throw the plane into snaprolls, spins, etc.

You will notice the low wing plane to be less sluggish in roll maneuvers. While the high wing plane has some difficulty making the first half of the roll, and after halfway it lurches back to the upright, you will find the low wing plane rolls more evenly.

The Twinstar has less dihedral and a more or less symmetric airfoil, making it more responsive in maneuvers. It will be much faster than your high wing .40 plane, even if you use .25 engines. Mine has two old bushing .40's, and it's a rocket. Engine-out flight is an exercise in rudder management and keeping the nose down.

Good luck,
Dave Olson