If you want a really strong 45-70, get a Siamese MAuser that's been converted.
I had one. And not the Navy Arms "carbine" conversion, a full size sporter with a conventional sporter stock, and a long barrel. Fine gun. Did have feed issues, took some tinkering but it did eventually run well enough. NO SERIAL NUMBER. Did have markings but nothing in arabic numerals or English letters other than .45-70 on the barrel. No idea who built it.
Also had an 1895 Marlin, one of the first of the modern ones that had the stupid crossbolt safety. IIRC conventional rifling. 385-400gr to 1800+, no problem, though it did kick a mite.
Still have a Ruger No.3, its my favorite .45-70. Max loads (for MY specific gun) run 300fps behind .458 Win mag. NOT for casual plinking, or shooting from the prone position, unless you have a desire to physical therapy, possibly after surgery...
its, short, its light, its accurate, has a great trigger and a lot of fun with loads at BP levels, and even with those, will drop any deer like it was hit by Mjolnir.
And, if you WANT something that will drop buffalo (and I'd include Cape buffalo with the right bullet,) the rifle will handle that, too.
The 350gr Hornady at 2200fps is really impressive. DON'T shoot the 400gr Speer above 1800 its not built for that.