I have killed the majority of my deer with a Marlin 1894 (16.5 inch barrel) I have used 140 grain cast all the way up to 200 grain bullets.
In my opinion 158 is the sweet spot. I like to use Flat point bullets over H110.
The Best factory loads I have used is the Buffalo Bore (both 158 and 180 grain) as well as the Magtec 158 grain SJSP
The range I get deer at is typically 35ish-80ish yards. I shoot them from my back porch using the rail like a bench. When I have to go and hunt I usually bring the 45-70 encase I see a Bear or a Moose.
Shot placement is everything! I would rather take a round of 50BMG to the foot than a 22short to the base of the skull.
all 26 of my guns are 45/70 govt, 357 mag, 22 or 12 ga... I believe in keeping it simple. Wish my wife did as well...