This is all quite interesting. I'm relatively new on this sight. I would only like to state that I have great respect for the ol' .45/70. I've owned a Marlin and Ruger #1. I liked them. The marlin [mine was a 1985 version] is the ne plus ultra for back-up /self preservation along a salmon stream, up in paradise.
Still nothing I could put in either of them [I load my own and have not shot Garrett's since it wasn't available at the time] would equal my Lott or my .404 Jeffery. I tried the Hornady 500 fmj's and every other bullet available at the time, in my Ruger #1, and that gun will take some pretty serious loads. When I say equal, I'm refering to penetration.
I'm not looking to take sides here, only to state my experiences.
There are people on this sight, as well as several others I frequent, that seem to be mesmerized by Randy Garrett's writings on his web. I don't know for sure, but I'd be willing to bet quite a pile of cash that most who talk about his loads are going strictly on what they have read over there and not on actual experience. His tests prove little. Wet paper is a piss poor medium, other than being easy to repeat.
I don't know any of you or your experiences, either on game or in testing your loads. I do know that not too many animals are made of paper, wet or dry. The only way to know what a given load will do is to use it on an animal, and there isn't a man alive who can kill enough animals with one round let alone several, to say which is best, or will out penetrate another.
In my opinion good is not always good enough.
Like I posted on another sight, energy doesn't kill. Big heavy bullets at reasonable speeds that have enough momentum to penetrate really well [provided they're constructed stout enough to do what you ask of them] , do this by punching holes in vital organs. However, over on that sight they were arguing about hardcast handgun bullets in certain cartridges, [.500JRH vs .500 S&W]. Here we're talking about higher velocity and with that comes the ability to start shocking animals somewhat. The .45/70 may penetrate like gang busters, but with little shock at the rather slow speeds of the Garrett loads. The bigger rounds have that edge, and in my own experience will penetrate any medium you want to shoot them into better than the .45/70.