If it were me, I would not have that drastic a difference between the hunting weight and the practice weight. If I planned to hunt with 50#, I would want to practice/shoot 3D with 40-45#.
I think with 5-10# difference, you could spend 2-3 weeks shooting the 50# bow and be fine. Of course, regardless of the difference, you shouldn't try to shoot as many arrows through the 50# or 45# bow as the 40# bow. If you want to do that, you should just shoot all your arrows from the 50# bow, which some people manage to do, but I have never been able (or wanted) to do.