Someone had given advice to take the lightest (weight not caliber) of the rifles you own. I am of the same opinion. Tundra is neither easy or fun to walk on. A pound either way helps, every little bit does. So, if the .308 is lighter, go with it, if its the 338, just as good.

I'd rely on a well constructed bullet, never hurts. Swift A Frames, TBBC's, NP's all work well.