I would advise a .44 Mag over the .45 Colt for a few reasons If you are using it with a companion combo, also for hunting.. (Note I love the .45 Colt round.)
1 No need to worry that a round too hot for most hand guns would wind up in the pistol by mistake.
2 Brass extracts easier for .44 Mag. The round was designed with a larger rim so that an extractor could grab it. (.45 Colt has a thinner rim part of the reason that Winchester did not make rifles in .45 Colt for so long. Also why so few double action revolvers are chambered in .45 Colt as well.)
3 .44 Mag is easier to find a double action if you wish to have one.
4. .44 Mag is easier to find at just about any store than .45 Colt, and is cheaper per box for the most part.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.