http://www.remington.com/ammo/ballis...s_specific.asp

This would be the best place to look. The 7MM RUM is a 404 Jefferys case necked doen to a 7MM bullet. Much more powder in this case. The 7MM-08 is a 308 case with a neck size to fit the 7MM. If you list them by most powerful it would be this

7MM RUM
7mm mag
7MM-08