Hoping for AR 10 advice.

[PFDD]

Not trying to be Captain Obvious here, but have you looked around Armalite's website? http://www.armalite.com/default.aspx I've ordered from them before and they're good to go. Granted you won't find a .300WSM barrel but uppers,complete rifles and lowers can be had. If you're going the customized route, I have a G.A. Precision AR10 in .308 that shoots bugholes and their work is highly regarded.

I've shot next to a AR - 10(T) Ultra .300 RSAUM that the owner was just starting to wring out. It was impressive but I think Armalite might have stopped production. There is a new .338 Federal chambering offered but I don't know anything about it.

If I was just starting to look for a new .308 AR platform over what I have, I'd go with the LaRue but you're looking to go the .300 route then that points you to the custom route immediately. Good luck on your efforts.