I agree with Mustad that 10X is a good binoc power for a caribou hunt..They have enough magnification to evaluate racks withing reasonable distances, but still are not so high powered that they can't be held steady... 8X works well also, and might be a little better ALL AROUND glass...

You find that your .270 is as close to a perfect caribou rifle as there is...Most of my caribou have been shot with my .280 Rem. which is very similar, and I've had great luck out to nearly 400 yards with it..

As far as shot distance is concerned, you can generally get shots at whatever range you are comfortable with... I have a Harris bipod on my rifle and like to watch from vantage points that allow a steady prone rest...I think every caribou that I have ever shot ( about a dozen) was shot with me lying flat on my belly on the tundra...I don't mind taking longish shots as long as I have a dead steady rest and conditions are condusive to good shooting...