BowWow.............. I think it depends on what your end goal is. Unless you say different, for this post, I will assume just having and owning a larger bore, maybe do some local hunting, and maybe do some shooting.
Big questions...... Do you Hand Load? If so, then you can increase your potentials a 1000 fold. If you hand load, I urge you to forget the smaller calibers and go straight to .458 caliber. There are literally 100s of bullets available in .458 caliber for many various missions. As Ronn says, 45/70 is great. It is. If you did not want to go the lever gun route, take a look at a Ruger #1.......... man, they are great fun. A Ruger #1 in 45/70 has tremendous advantages over the lever version, and you can damn near dupicate 458 Winchester ballistics if you wanted, or you can down load to 1000-1200 fps and have a big fat slow bullet, no recoil to speak of, and have a lot of fun with it. Decide to do some hunting, you have so many wonderful bullets to choose from it is staggering.
Being a fan of the 45/70, there are other options past a Ruger #1 for a strong action. Please meet the Siamese Mauser, a bolt action 45/70 in the classic Mauser action and extremely strong. This rifle coupled with handloading prowess insures that the hunter will never be undergunned on the North American continent and probably very adequately armed elsewhere and unlike the #1, there are several followup shots in the magazine at the ready.
But lately I've been going very old school on a big bore- 50/70 in a Remington Roller with tang sights, Hadley eyecup and spirit level equipped front globe sight. Yeah, it doesn't have, nor is capable of power levels the Mauser can get to but sometimes it's just cool to be launching 400gr boolits with real black powder. Sorta like driving a classic car that hasn't been molested.