I think you'll find the case capacity of the 45 Colt more than addaquate to do what you are looking for, most guns just can't stand the pressure and the guns that can just aren't designed as a defensive weapon.
In comparing to a 44 special, well, a 250 grain bullet at 850-900fps should speak for it's self. Black powder 45/250's run between 750-800fps, if memory serves me correctly.