That’s a .45/70, its sole job is killing whitetails in the brush. I would probably take it if I were to go buffalo hunting though. The challenge I’m looking for on the next trip is to put a “booner” on the ground.
I am a dyed in the wool 270 guy. They are hard to beat for about everything you can think of in the lower 48 with the proper ammo. But I don't really like them in anything under a 24 inch barrel. Critters don't know the difference in the few inches but its a mental thing for me.
I love a 308 but feel like I'm over gunned when I use it for Pronghorn. There's no reason to feel that way I guess I just do. A man is entitled to a few unwarranted opinions.
I know it wasn't on your list but the 25-06 is a magic stick when it comes to pronghorn albeit a little light for elk but many have been killed with it.
At the end of the day however, the 7mm08 as far as weight goes fits the bill, since you're wanting something light and with a 20-22 inch barrel. You already know the affinity people have on here for it and for good reason. Its a wonderful cartridge and being a short action comes in lots of light rifles. I have 3. 2 savage axis for my daughters and a Ruger RSI Mannlicher. None are over 6 or 7lbs. As far as using it for the occasional elk...well, there's been a few elk killed with it since it was released around 1980.