Cant decide on a scope for my AR 308 build. Im going back and forth between a Leupold VX-2 3-9x40mm and a Vortex Diamondback HP 3-12x42mm. Will the side parallax adjustment justify picking the Vortex over the Leupold or is the side parallax adjustment not as important? Rifle will be used for target shooting paper and steel targets at ranges from 50 yds all the way out to 600 yds. Barrel is 18" long with a medium length gas system.