Vltor uppers are nice, but of the several that I've used, none were are a snug fit on a variety of barrels, slip fit at best.
So if you really like Vltor uppers, trueing the face & loctite is your friend.
As for lightweight barrels that shoot well, Wilson Combat barrels shoot well above their price point weight, especially when on sale. Pretty much as good as my Craddock's. And they don't foul.
MM