I load and shoot both the .45-70 and .45-120 Sharps cartridges. Both of my .45-70's are Marlin lever guns. One is an early 1895 and the other is a new 1895 Cowboy Rifle.
My .45-120 is a Browning B-78 that was re-barreled to .45-120 Sharps, with an octagon 24" heavy barrel.
When loaded to full capacity, both rounds will bring tears to the eyes of an inexperienced shooter if they don't know how to mount and shoot a heavy recoiling rifle. I've only seen one person, other than myself, who would shoot more than a few rounds from the .45-120. A female Game Warden once put 21 rounds through it in one session. The most I've ever done in one session was 75 rounds of full power loads. I use a 420 grain cast bullet with gas check, at over 2200 fps in this caliber, and it hits with authority.
For the majority of my hunting .45-70 loads, I use a 405 grain Remington JFP bullet, loaded to 1850 fps. This is a full recoiling load in a light 1895 carbine, but does the job on large game. The biggest animal I've taken with it was a Canadian Moose, which only took one round to put down at approximately 125 yards.
For the 1895 Cowboy, with 24" barrel, I've settled on a lighter 330 grain bullet loaded to a leisurely 1300 fps. It's a comfortable load to shoot and is very accurate up to 200 yards.
If I were going to purchase only one rifle in this catagory, it would be chambered for .45-70, and have a strong action, such as the Marlin. This round will take any North American game animal, with the proper load.
Hope this helps.
Fred