That speed seems too high for a .45-70,even out of a Ruger. I have a Ruger .45-70. Also had a Siamese Mauser and the 1895 Marlin (not the guide gun). I know the limits to the strongest .45-70, and 2300fps with a 400gr bullet is beyond them!! At least with a normal length barrel.
Pushed to the max, and UNSAFE in any other gun, I can just hit 2200fps with a 350gr bullet in a Ruger .45-70. 2300 with a 400gr bullet is .458 Win mag territory, NOT hot .45-70. The modern Marlin, with a 22" tube can run 400s up to about 1800fps at max, and its not even remotely a joy to shoot.
While you can put even hotter loads in your Marlin, what you can't do is get the fired cases out, other than one at a time with a rod. And that pretty much negates the value of the repeater.
people have been dropping moose and bison with 45-70s at black powder
speeds since 1873. I haven't seen any "study" indicating that animals are any more bullet resistant now than they were then...
Plus, while you can significantly up the speed of standard factory loads, you need to be sure to use the right bullet. Speed makes an excellent 400gr slug for the .45-70, but it is built to give controlled expansion at black powder speed (12-1300 fps) and will definitely come apart in an uncontrolled manner if pushed over 16-1700fps. Been there, done that, seen the slugs. And, that same bullet at 2100fps from a .458Win Mag acts very much like a varmint bullet.
The Hornday 350gr is built differently and does hold together well above black powder speeds. Other bullets are similar, some will handle much higher speeds, some won't. Some research is required to match the right bullet with the right max velocity.
Nothing will make the .45-70 shoot flat, and to me, its not worth beating yourself to death to reduce 48" to 42" at a given range. If you can compensate properly for one, you can do it for the other as well.