Real world, not much difference in the rounds. You're going to have to split hairs (.007 of an inch to be exact) to find a difference. It sound like you've decided on the 270, but if the 280 is NIB PM me I might have a buyer for it. I'm a big 280 fan, and have a few buddies that are as well and some are always looking for a gun. On another subject either of these calibers are plenty for long range whitetail (I can personally attest that a 280 is a hammer on shoulder shots at 430 yards), so you might want to think about just bringing the 270 as it should be plenty capable for the Kansas hunt.

Gordon