Shooting steel is not as critical but just remember that you need 900-1000 foot pounds of energy to get the bullet to do its job on a 200 pound animal. That number can vary slightly depending on who you ask. Maj. John Plaster subscribes to 1000 ft. lbs. I would use that as a guide in your bullet/cal. selection as that is more critical when killing game. Of course bullet placement is a big part as well. Of all the calibers listed Mojo Hand has it right with flip a coin. I personally would opt for the 7mm-08 as the BC is better on the .284 as opposed to the .308 and has a very good bullet selection as well for the reloader. Ballisticsto suggests that 550 yards with a 120 grain bullet is no problem for deer with the 7mm-08. I can tell you from experience that it performs fine. Just my 2 cents.
Anyone using foot pounds energy foot pounds energy to rate lethality hasn't a clue. Sorry that Palster fits in that category.
I have killed too many animals with much less energy and complete penetration.
