I have but one 45-70, a Marlin 1895 GS and as previously noted just about any loading will easily take deer. My go to loading is 50 gr. IMR 3031 under a 300 grain jacketed soft or flat point usually Hornady but any brand will work just as well. I have gone up to 460 gr. lead flat points in the 1600 fps range but it is just too stout for me in that light of a gun (and no I am not especially recoil shy as I routinely shoot 338 LM and 300 WM without a problem, but in heavier guns).
Anyway, my answer is 300 gr at about 1600 fps and forget about it and put some venison in the freezer.
Gary