These are such good honest airplanes as designed. They are fun to fly and will take a beginner quite far into more advanced flying, before he becomes bored with it. The step up in size might be fun to do. 10% isn't really adding that much to it's size. I'm sure a .60 will still handle the plane well. I'm uncertain if there is a benefit in taking out the dihedral. I guess you won't know until you build it and fly it.