I have a 4.2" Redhawk in .45 Long Colt and, as has been said above, it will handle any load available.
As a handload, I have a load that will get a good honest 1250 fps with a 275 gr, hard cast bullet.
I wanted to provide the specifices, but that file seems to be corrupted somehow. I will have to take the flash drive to my guru to see if he can salvage it. 8)