RE: .270 or .25-06?
I own a 25-06 so yeah I'm a tad biased but I love it. You won't see any disadvantage on deer compared to a 270. A 270 won't do anything to a deer that a 25-06 won't do except kick you more when you shoot him. A 25-06 with a 115 grain nosler partition is deadly on deer sized game and shoots just as flat as a 270 with a 130 grain bullet. I can't imagine a better open country Antelope caliber than a 25-06.
If the choice was deer + bigger game I'd say 270 because of it's ability to handle a 150 grain bullet if need be, but if you want a caliber for whitetails, muledeer, antelope + possibly varmits I'd say 25-06.