I haven't made a big jump back and forth in weight like that. For occasional form work the 45 will be good, but I would still do the majority of the work with the 65.
I have gone from 51 to 42 but never a 20 pound difference. If you are going to shoot the 65 for hunting then I would make sure I had plenty of practice with it for consistency sake. Your release will be VERY different from 45 to 65. The 65 pounder should give you a better release or at least that is how many guys feel. Heavier bows = cleaner release is the theory. I would continue to shoot the 65 pounder, but just go easier. If the elbow is still hurting after you scale back some, then definitely go to the lower weights or a bow with a more ergonomic grip. Also the arrows will shoot flatter from a 65 pound bow than a 45 pounder. You could mess with arrow weight to get similar trajectories, but I wouldn't want to fool with it personally.
All that being said, shoot the heaviest bow you can with a few qualifications;
1. Make sure you are accurate with it.
2. Shoot it a reasonable number of times with rest as needed. Just like working out.
3. If the draw weight is causing you to have pain, then draw less weight or switch to a different grip. I had elbow pain and it turned out that I just needed a different grip.
4. Don't worry about what draw weight other guys shoot. Just shoot the draw weight that is right for you.
If you are a pretty strong guy, and I suspect you are, then I would do my form practice with the 55. If you find a REALLY cheap 45 pounder then it won't hurt, but you definitely need to be shooting the 65'er consistently if you want to hunt with it.
Good luck!