The first question that I have is are you talking about the speed in which the airplane rolls? That really and as speed decays on an upline and you start loosing some aileron authority is about the only thing that the aileron cord is going to affect. To obtain really good axial rolls requires that the airplane be set up correctly at multiple points. It will require some measuring, changing of the wing incidence and most likely a CG change. It will also require a number of test flights. I of course would be more then happy to get into greater detail if you want. I only ask that if I take the time to do so that you are ready to give these things a try.