A large-framed Ruger .45 (and a few others) can be overloaded to exceed the energy of factory .44 Magnum, and the .45 will do it from a shorter barrel. But if you have a large-framed Ruger .44, I'm sure you can safely overload it too -- but I'm not sure how much.
Do not try to load .45 Colt to .44 Mag pressures! You don't need to. .45 at about 25000 psi is equivalent to a .44 at about 35000.
.44's tend to be more accurate too unless you have a custom .45, because the chambers are reamed tighter. I was going to say the .45's have sloppier tolerances, but I think the proper term is "clearances"