Magnification isn't as important as glass quality/clarity and repeatable adjustments. The rule of thumb for "tactical" shooting is that 0.5x to 1x per 100 meters is perfect when it comes to magnification. There are a lot of snipers out there who like more magnification, but usually for the observation portion of their mission instead of the shooting portion.
With a 26" barrel shooting 308 you'll need around 40 moa of UP from from your 100 meter zero to get out to 1 kilometer depending on atmospherics. Off the top of my head it should actually be closer to 35 moa, but you'll want some padding. That limits your scope choices a bit.
Machine guns are awesome until you have to carry one.