You know the saying "size dosen't matter" well it dose.So when you throw game in the mix over 800lbs and tooth and claws also.I would say go with biggest caliber you could shoot.
The 270 is a fine deer rifle IMHO(although I like the 25-06 better) it has worked on lots of big game.It's not my choice for elk or moose I like the 280 Rem as a min. 30-06 is good also.But when BIG BEARs are tossed in there I would like alittle more punch.I would say at a minimum 300 H&H(30-06 also) and the 300 Win Mag.

Jack Occonor once wrote that the lowly 35 Rem was a good Griz gun with 200 grain Core-loks,you know I will just take his word for it and stay with my 338 Win Mag or 416 Rem if and when I go after griz.

So to answer your question is the 270 Winchester big enough as a all around gun? In my eyes NO but you don't have to take my word for it,if you think it is then go for it.Let us all know how it turns out.

Oh and if you are planning on hunting in Alaska and Canada ALOT go stainless and synthetic.

Good luck and safe hunting.
BBJ