Another vote for the .35 caliber. I have owned a custom Mauser in 35 Whelen AI for almost 20 years now, and have shot loads from 158 gr cast lead at 1400 fps (bunny load) up to 275 gr Hawks at 2450 fps (grizzly load). My long range load is a 225 gr Partition at 2720 fps, which has the exact same trajectory as the 180 gr Partition in the 30-06 out to 400 yds.
The minimum taper and sharp shoulder make for excellent brass life, and none of my loads take as much as 60 grs of powder, so it's not too expensive to shoot. If I was not intending to hunt the great bears with it, the .358 Winchester would be even better-- lighter, shorter rifles and even more efficient on the powder.