Is being able to buy factory ammo in the US easily a major concern for you or not? If it is than sticking with 30-30 or similar would probably be better for you.

If you are OK with hand loads then I personally think either: the 7x65R, or and the 8x57JR would work well. As an earlier poster mentioned for close range work in driven hunts the 8x57jr is quite common in France (and I would imagine other places in Europe) for wild boar, red stag and roe deer. I've seen lots of game fall to this cartridge even though I do not use it myself.

I am a big fan of the 7x65r and I use it extensively for most of my hunting. I have a drilling and single shot in this caliber. Its flat shooting, accurate and with minimal recoil. I'd pick it just because I think its more flexible for longer range shooting, though with your double rifle you might not be considering a great deal of long range shooting.