Actually, in "identical" revolvers; the .45 Colt can be loaded heavier than a .44 Magnum. I have some pressure data from John Linebaugh and Hogdon that indicates a .45 Colt can move a similar weight bullet to a .44 Magnum at slightly lower pressures with about half the barrel length. The .44 Magnum generally has to work 4,000-5,000 psi harder to acheive similar velocities.
Now, theory and reality being what they are, you did not state what you intend to do. If you are hunting deer or bear and nothing larger, either will do just fine without loading heavy. Each firearm is a law unto itself and some shoot accurately across the entire power spectrum. Others may shoot more accurately on one end or the other. There are several variables that influence accuracy; not the least of which do not pertain to loads but shooter technique.
If your game is shooting big heavy slugs, I'd say go up in caliber and not powder charge.