About 20yrs. ago I had a Marlin 444, and a S&W 624 x 4"; thought the same thing about 'consolidating projectiles', etc., but it didnt really pan out that way for me. If I loaded the 444 down to about 44M equiv. loads it was OK, but if I made factory equiv. loads, or upped it to 265s it was an abusive rifle, even with a recoil pad. OK, it has a trajectory advantage over the 45-70, but with a heavier 'brick' out of the old service round, even at slower velo and more loopy traj. it just does the job and I dont feel beat up. To get that kind of energy out of the 444 it wasnt pleasant. I sold it, a glorified 44M fit a hypothetical hole in caliber spread that I didnt really need to fill.
Of coarse, if I had a 444 and no 45-70 now I maybe wouldnt feel the need to switch everything out, but having the 45-70 I wont go back.
As a wise man once said,"dance with who ya brung".