I fly the 51 (D and to a lesser extent B) whenever it comes up and I likes it
Best cockpit view, excellent control response at all speeds and .... speed.
I think it handles reasonably well regardless of fuel load. The cg or weight or whatever shift is noticeable but unless you are a stick yanker it's nothing to worry about. All it takes is practice. I've noticed that after flying the 51 I tend to fly other planes in the same way, that is, smooth and coordinated control movements, no continous tight turns, etc. and it actually helps a lot and feels more natural.
Perhaps it's the handling of the other, presumably easier to fly aircrafts that needs to be fixed
