I have seen good bullets put a deer down with both calibers and also heard of lost game with both. Range and killing power is limited with the two magnums and trajectory is a factor if longer shots are desired. Barrel length helps get the velocity up....probably at least 300 fps faster in a rifle over a handgun.

I started out with a muzzleloader and always looked at 1000 ft lbs of energy as minimum and the 44 mag is right there. I have seen other opinions that 600 ft lbs is bare minimum which gets the hot 357 mag loads. The 44 mag rifle is adequate in power when good bullets are used and ranges are reasonable, but you're right shot placement is the key.