This is debated to death, but it seems that the different sides never really listen to each other.
There is a difference between an adequate hunting round and an adequate DG stopping round. They both have a place and mixing the 2 causes arguments.
a 45-70 is not a DG stopper. The gold standard for a DG stopper is the 470 NE (2150FPS 500Gr 5000ftlb). If your gun/ammo is not at least this, it is not considered a stopper period end of discussion, 100 years of history don't lie. The advantage of a stopper, it will drop anything that walks inside of 75 yards. For some animals, that means a near miss will usually produce enough concussive effect to slow things down a bit. That's when you see elephant head shot but miss the brain, but they still fall long enough for several follow up shots that will hit.
The gold standard for adequate hunting round is the 375 HH (2300 FPS 300GR 4000ftlb). This is the legal minimum.
Now the confusion is the 45-70 is a true big bore (above 40 cal). But since it lacks case capacity, it can neither drive a heavy bullet fast, nor a light bullet with a high enough BC to make it compete with smaller dia calibers.
Is the 45-70 suitable for DG, well in my opinion it is on par with a 375 inside of 100 yards. Look at factory ammo comparison:
45-70
Buffalo bore 350 gr. J.F.N. (2100 fps / M.E. 3500 ft. lbs.) (in guide gun, likely 100-150fps in a 22 - 24" Bar.)
Grizzly Ammo 400 gr. PUNCH W.F.N. (2000 fps / M.E. 3600 ft. lbs.) (in guide gun, likely 100-150fps in a 22-24" bar.)
300HH
Federal 300 gr TBX (2470 fps, ME 4064 ft lbs) (in 24" barallel)
Federal 300 gr TB solid (2470 fps, ME 3966 ft lbs) (in 24" barallel)
I have not seen anyone disucss these 2 relevant comparisons in a fair dis-passionate manner, I have heard how the 375 will shoot farther thus negating the effectiveness of the lever gun. Duh, it's skinny and fast, that doesn't prove anything regarding the stipulated limits (which are reasonable) above. With good bullets i can't see how a 375 can be considered utterly world class and a 45/70 touted as a stunt.
To answer the 45/70 DG fanatics out there, there are photos of probably a dozen guys out there who shot elephant and other big stuff, lets say 25-50 in the world since the 45/70 has stepped foot in Africa. the classics (470NE, 458WM, 416 class) have killed thousands upon thousands, there is no comparison to make here, regardless of who is making the claim, but some Phs on this site do not have to be stuck-up ish when stating the obvious (some have been highly responsive with great positive feedback, you know who you all are).