USAF might get GEnx 747'type engines for the same price and get the original TF39's cruise SFC that they don't get with the CF6-80C2. They have to pay again for a new nacelle but it might be worth it and GE should have ample of engines that can be derated and be military certified during the new nacelle design/build/certification time.
Just call int the C-5M2...