There is absolutely no reason to consider the magnums given your criteria. If you reload you could always load the 300 or big 7 to 308 velocities but if you are buying ammo off the shelf the 308 will do fine. The 270 will do the job equally well and that is my choice because some of my hunting involves long range shooting and the extra velocity helps flatten trajectory but inside 300 yards there are lots of cartridges that will get the job done.
