I think you should choose a RIFLE action first.

If you have a short bolt action you should look at the 260. If you have a Mauser length bolt action I'd use the 6.5X55
If you use a long bolt action I'd go with the 6.5-06 or maybe the 264 Mag.
If you want to use a NATO length detachable mag (autos, and some bolt actions) go with the Creedmoor.

If you are going with a lever action BLR or a BAR use the 260.

Use the RIFLE you want and learn the trajectory of the load. All are just fine.