RE: .30-06 vs. .338 win mag vs. 300 win mag
For anything but Grizzly/Kodiaks/Polars, I'd pick the .30-06. I'm a bit recoil averse, and really don't even like shooting my 06. I've switched to a .243 for deer hunting...
If I was going for big bears, I'd take a close look at the new .338 Federal rather than the magnums you listed.