One use for the longer range, if you're skilled enough to pull it off, is in the admitted very unlikely scenario of a Red Dawn type situation. You're in the position of trying to snipe at range, and thin the invaders out, without getting too close and getting decisively engaged. Pop one or two at 300-400 yards (600 for the very skilled), and fade.
I don't think this kind of scenario is very likely - it's damn unlikely, but not impossible. Say some rogue nation, like N. Korea achieves orbital capability, launches a couple "sattelites", which turn out to be nukes, and EMPs our asses. The Mexicans decide it's time to get back at us, and hordes of people invade North. I know in such a situation, the extra range capability would be useful. Not that I could hit anything reliably beyond 400 yards, but some can.
No psycho thinking here, just keeping the options open.