I thought the main purpose of the larger fuse was for handling purposes. Like better roll rate, knife edge performance, etc. And best of all, I can get my hands in the dang thing to work on stuff.

AS for slowing it down... I think the throttle is the most important followed by wing drag(thickness) and prop choices. Wing drag you can't control unless your desigining the airfoil of the airplane.
Look at the fun fly airplanes with wings as thick as a brick yet they have a profile fuse. They will fly very slowly due to the thick airfoil.