There is a very good article in the latest Field & Stream called, "Dinner Bell Grizzlies." Well worth the time to read. Makes it easy to understand part of your problem.
The lightweight rifle is also something to consider but if time permits I would consider the 30-06 above the other cartridges. First would be the availability of ammo. The 30-06 is probably going to be easier to find at some backwoods store. Take the time for the wife to shoot the rifle with comfort using lighter loads and working up to a proper weight bullet for bear problems. The 180 gr. Nosler at top level velocity should work just fine although personally I would use the 200 gr. Partition for the potentially better penetration. Replace the factory recoil pad with a Pachmeyr Decelerator. They really do work. If you go to the Nosler forum, school down to the published load data, then check out some of what relied 17 does in the old 06. I'll be playing with some of that stuff and the Nosler 180 gr. Partition in the very near future.
I know that most US made 8x57 is pretty darn wimpy so it would have to be a strictly reloading proposition. A 200 gr. load moving out at a decent velocity would definitely get a bear or bison's attention. Never played with a 7x64 but have done some work with my .280 Rem. Recoil with 175 gr. bullets wan't all that bad but the rifle is very heavy for a sporter running close to 10 or 11 pounds ready to hunt. Gunsmith decided to use a barrel as big as a telephone pole. Beautiful rifle but needs a set of wheels.
Paul B.

Our forefathers did not politely protest the British.They did not vote them out of office, nor did they impeach the king,march on the capitol or ask permission for their rights. ----------------They just shot them.
MOLON LABE