Well I'm no ballistics expert, but I have done my homework. No matter what you load in the 45/70, the .458 Win Mag will out perform it when the pressures are kept within acceptable limits of the rifle. IE. Ruger #1. The .458 Win Mag case is much stronger than the 45/70 case and thus will handle pressures better. Extraction will be more positive by a corresponding reduction in possible stuck cases. 300 fps does make a difference in penetration on game. Especially DG. Some calibers even need a reduction in velocity to achieve deeper penetration. The bullet used in these ultra velocity big bores actually tends to tumble and break apart. This is due to manufacturers jacket thickness for the same bore. A bullet cannot do all things at all velocities, so they make the bullets to perform as designed within a certain terminal velocity . If this TERMINAL velocity is not achieved because it is too slow, or it is too high, the bullet will not perform as intended or engineered. I want the bullet to act as it was engineered on DG. I'd use a caliber with a velocity in the mid to high end of the bullets range of operation, in case of a bit longer shot being needed. I'd forget energy, trajectory, and ballistics merits of any other caliber comparisons and concentrate on the one at hand. It has been proven time and time again, that a quality 480-500 gr .458 bullet needs to hit an animal at 2100-2400 fps for ideal performance on the game. If using solids, the same applies for the bullet to travel the straight line path into the vitals or brain without deflection due excessive speed. If you need a vehicle to go to work, a similar Chevrolet works just as well as Ford, both are the necessary means to an end. Why not just use the tried and true calibers or ballistic equal instead of endangering yourself, the PH, or his trackers unnecessarily. This does not make any sense to me. Just because it might work some of the time, might work most of the time, is not reason enough for me not to use a weapon and caliber that works every time.