I've used my 270 for basically all of my hunting and have taken sheep, moose and elk. I personally shoot the 140 gr Accubonds. I think you'll find that the people on this forum will be evenly split betwee a 270 being enough vs. not enough cartridge. Shot placement, knowing your limits and bullet construciton are probably the most important factors. I've seen guys with 300s or 338s think they have more leverage with shot placement by shooting a bigger gun.....not the case.

For brown bear, I agree with the others, you want to shoot the biggest thing you can comfortably shoot. Some outfitters won't even let you take anything less than 30 caliber. But then, how often are you gonna hunt griz?