In regards to .270 not being enough for big bear, I believe it would be. If it is what I had, a 150gr Partition, A-Frame, or TSX would be my choice. If I were able to afford a new rifle specifically for a griz hunt, truthfully I would probably go for a Ruger M77 in .338 Federal or a CZ550 in 9.3x62. As it stands, my hunting rifle is a 7mm Rem Mag, so that would be my choice.
Would I want a deer-centric bolt action .270 with light construction 130grs in my hands while being charged by a furry flurry of anger in griz country? Hell no.