I've done a couple of NCR playhthroughs before where I just help everyone but stick to the main story of the NCR. On this playhthroughs I'm strictly only doing NCR interests. Now I've just got the mission to deal with the great khans. Now back at boulder City I killed them due to lacking other options. Now would a true NCR patriot ally with the Khans to make them stronger, or would he destroy the Great Khans to remove a great thorn in the NCR's side and cut fiends supplies?