Hey Bart,
A 22-250 IS ballistically superior to the 223 if you are looking to shoot greater than 300 yards. In my eyes, the 223 is an economical, readily available cartridge that can pretty much handle everything a varminter would want out to 300 yards or more. For me, it's the 30/06 of varmint cartridges! Pretty much will work in pretty much every situation for which it was designed and in some that it wasn't. If I was doing allot of long range prairie dogg'n, I'd get the 22-250.
The 45/70 is also a great round that mostly will be used at the shorter ranges on rather big animals. For that one, I'd go ahead an buy what I liked. Currently, I have #1. I had a 35W in the Rem 750 and I liked that gun allot but the accuracy was just dismal. Worked just fine, never a jam...but couldn't get much better than 6" groups at a 100 so I traded it for a 700 CDL in 35W and took it to TX and killed that Nilgai in my avatar and an oryx.
Whooppee!! Never have enough!!!!