Nothing like reading a good flame war when I get to work at 5am
The perception of what we see as a big bore has to do with what we will be hunting with it. I don't know why in the heck africa all of a sudden became the main focus of this topic, jake just wants a big gun.
The reason most people don't think of the .45-70 as big bore is because there really isn't much special about it. It is a tried and true round which a lot of people hunt with. It won't take a rediculous amount of powder, but in its lifespan, has killed a rediculous amount of game.
Jake, are you going to go elephant hunting? If so, the arguements here have basis. If not, go by what you like. The .45-70 has a big meplat, isnt going to impress a whole lot of people because of how many there are out there, and would be good for general shooting/hunting. If you want to impress people, that is when you step up to the .458, the 375 mags, the .416 mags. And if you dont call the .416 a big bore... you need to go and shoot a .416 weatherby.
Heck, to some people, even the .458 is becoming small potatoes, with the increasing popularity of the massive bores, like the .50bmg, .416 barrett, .577 tauranasaus, the NE cartridges, 460 weatherby, anything used for real hunting is almost automatically not a big bore.
Overall I would decide if you want something which you can shoot often without hurting yourself, or something you can shoot every once in a while, but have everyone at the range wondering what suddenly made the wind come up.