Re: 7mm Rem Mag vs 6.5mm Creedmoor
What distances are you planning on shooting? The creed could take you to 600 yards for game and the 7mm Mag would take you to 900 or so with more authority. Maybe a little further with the 180 Bergers.
The 7mm would burn more powder, have shorter case life, and burn the barrel out quicker than the 6.5 creed.
Depends on whether target or hunting takes priority too. Maybe you should get two rifles. Get a Savage 6.5 Creed or similar for target and long range practice and go hole hog on that 7mm and the defiance action. That way you have some backup if one rifle is down for some reason and you wont be burning up an expensive custom long range magnum rifle at the target range. That's probably what I would do.