Brian:
If I were to pick a caliber for whitetail hunting in a double gun within your choices I'd go with the 7X57R. You didn't indicate where you would be hunting and the 30/30 is a tried and true deer rifle in short range Eastern conditions but the 7X57 outperforms it in just about every category. IMO The 8X57 is really going to pack a recoil wallop in a rifle of that weight(6lbs9ozs) so I would pass. If you are planning on hunting in the Western States where the ranges are longer a double in 7X57 could also be used for Mule Deer hunting. It wouldn't be the optimal choice of a rifle for Western hunting but it would certainly suffice and,I personally, would get a charge out of bagging a deer with a double rifle.
Let us know how this turns out.
As an aside: The 7X57 is still a formidable caliber and remember that the African hunter "Pondoro" Bell killed hundreds of elephants with a rifle chambered in 7X57.
Jim
