Oupa,
I don't know what you guys out east hunt, but here in the midwest, the 45-70 will do a great job on anything I am going after. I built a lightweight double barrel 45-70 for deer hunting (eight pounds scoped with 26 inch barrels), and I use 300 grain hollowpoints in it at around 1600 FPS. It is more than enough for any hog or deer, and would handle one of our rouge Mountain Lions very handily. I could push this bullet faster, and I have a few times, but it is not necessary. I have also used 350 grain flatnosed bullets and they shoot to the same P.O.I. as do the 400 grain cast.
If you want to have a fun gun to hunt locally with, one that isn't going to wear you out carrying it, or pound you half to death shooting it, then you have the right idea. I think the 45-70 will give you the most bang for your bucks and you will enjoy shooting it as well. Some of us are never going to go to Africa to hunt but we do like to have two quick shots available when things don't go as planned with the first shot.
If my eyes were better, I would not put a scope on a double rifle, BUT, it is necessary at my time of life to have some visual aid if I am going to keep hunting efficiently. I would not feel comfortable hunting deer with any gun that I couldn't handle well enough to be almost sure of a one shot clean kill.
I too considered such bigger 45's as the 45-90 and the 45-110 and 120. They didn't offer me anything that the 45-70 couldn't do cheaper and lighter. With modern powders and a good stout double, you can work up loads that will exceed the old 45-90 loadings, so why bother and also spend more money when the added horsepower is not needed or used? These larger calibers were not meant to be Express calibers, they were meant to shoot heavier bullets than the 45-70 at about the same speed. You don't need the extra bullet weight, or the extra recoil, believe me. Bob H.