For a .338 Fed AR, the longer 18" or 20" barrel isn't going to do anything for you that's beneficial. Well, besides add swing weight to the gun. For hunting, and 250 yards, the 16" is overkill, in a way. Best scenario, even for another 100 yards on top of that, without building a shorter barrel and ending up going the SBR-route. The 16" is the way to go.
Here's my mantra on barrel length... If you have an accurate gun, it's always going to be an accurate gun. If it's an accurate 20" gun, and you want to cut the barrel down, it's still going to be accurate. Barrel length only affects velocity, not accuracy. And, a shiitty barrel is always gonna be a shiitty barrel, no way around that. The WC barrel that you're looking at IS an accurate barrel, and it's one of their match barrels - it has all their tricks, including final hand-lapping. That's why I think it's worth waiting for it.
Post up your list of parts when you have time, and we'll look them over and see what's listed. If something isn't going to work, or there's a better part out there, we'll see it in the list. Short-cut the long-term diagnosis that way.