I have a Remington 700XCR in 338 Lapua. I am needing some help on mounting a scope on it. I want to shoot it at 1000+ yards. I am looking at a NightForce scope, either the 8-32X56 or 12-42X56 NSX scope. I see there are two different rails available to mount the scope to, the 20 MOA and the 40 MOA. I have no idea which would be needed for the 1000+ yard shots. Also, I do not find a chart to tell me what height rings to use to mount it. Any advice would be greatly appreciated.