Dylan, I have the Marlin in 45-70. Awesome rifle. As far as shooting deer, it doesn't do any more damage than my 12ga, 30-06, or .50 cal. Shoot them in the shoulder and you do damage, through the ribs and you waste less.
I handload for it. Lighter bullets, higher power rounds and it shoots about an inch at 100 yds and the recoil is less than my slug gun. The recoil is different than my 06 or slug gun and is more manageable than guys would think. Do a Sims custom fit pad and you will be happy.
With just factory loads, it is comparable to a slug.
Last I looked, the Marlin would be the better choice if you might handload. I think it was a stronger action than the Henry. There is different pressure tolerances between different actions and ages of rifles. That is why most factory ammo is lower pressure to be acceptable in most good condition rifles.