My Christmas gift this year from my family is a riffle. I have already decided on the rifle I am going to get. It is a Rossi Wizard. This is similar to a Thompson Center as it is a break action that you can buy different barrels for. I'm a sucker for single shots. Now I just need to decide on the calibers. I want a caliber for shooting deer under 75 yards as that is what 90% of my hunting is. Then I also want a long range caliber for Deer and Black bear. For the short range I am torn between the 45-70, 357 magnum and the .243. I like the .357 and .243 because they are lower energy, very common ammo and I already have guns in those calibers. However I find the 45-70 is just plain cool. For long range I am torn between the .270 and 30-06. I like the .270 better but the 30-06 is more common ammo.
There is no comparison between the .357 mag, .243 & 45-70. Fo close cover clout, there is no substitution for frontal area. Simply pick up a .243 cartridge, a .357 cartridge & a 45-70 cartridge all at once in your hand and then ask your self which you'd rather have when you track the bear that ran off after the shot and then look in a mirror. You'll have your answer quick enough. I own two 45-70s, 2 .450s and a slew of other mediums too. They are not the monsters most make them out to be. My last buck I took two weeks ago was with a .450 Marlin shooting 350gr @ 2150 FPS. Bang/Flop.
At the ranges you are talking for the short-range barrel, standard factory ammo in 405gr @ 1300 FPS or 300gr @ 1800 FPS will do a bang-up job for you with minimal recoil
. If you want more horsepower from the 45-70, get some loads with a 400gr @ 1800 FPS if you want ($25/box). It will recoil stoutly, however. I shoot a 325gr bullet at 2150 FPS in my Ruger #1 45-70 and it's not bad at all (that's the LeverEvolution ammo) and a 400gr @ 1800 FPS in my Marlin 45-70.
I'd think the 45-70 to be an absolutely great choice for you and that rifle for your short range desires. As for a long-range cartridge for deer & bear, between the .270 & '06, I'd choose the larger frontal area and heavier bullets of the '06 for bear, again hands down. The ammo choices and availability for either the .270 or '06 are numerous and no problem finding either anywhere they sell ammo.
Good luck and enjoy that nice new rifle when you get it!!