I am not going to get into the 45-70 argument but I will query one of your comments.
"As for having a PH back you up, I see no difference in a PH backing you up when you use a Marlin or a double 577 NE."
A 577 NE (and a 500 NE) slightly off from the brain will still stun the animal enough even if is not a killing shot. I don't think the same could be said with a 45-70 at the fps you are talking about - or even a .458.
The effect of ANY calibre.500" and over is significant - at the correct velocities.
500 Nitro
Edited by 500 Nitro
45s_save_lives Regarding your comment" "I am not sure how famialiar you are with bison but they are much larger and tougher than buffalo,, african or asian. They weigh a hair over a ton, have a thick winter coat of fur and a thick layer of fat. In the case of bulls they are also very mean and cantankerous."
Everything you say (exept the thick winter fur) applies 150% to the Water Buffalo Bulls we have here in Australia.