You might find some words in the big U18 threads.
My vague impressions from the two games on TV (vs. Canada and Slovakia)... Shattenkirk seems a lot more rounded than some of the comments I had heard about him before? He is the go-to guy on D for them, captain, quarterback, all-round leader. It's fair to expect McDonagh to have a slightly tougher time suddenly stepping into basically a set lineup, and stepping up to a higher level of competition than he's recently been facing. So what we see from McDonagh is more like "flashes" of his ability to move with the puck and play bigger than he looks physically. Both have impressed me, though. It has been nice to finally see them. I can understand top-20 predictions for them (and even those ones who say that if they're a certain team's "favourite" they can challenge for top-10).
Conversely, Tommy Cross looked to be rather more challenged to keep up at this level to me.
Still, any team scouting these guys is going to be going on a whole lot more than this tournament. So they'll have their reports on McDonagh and Cross from before, and they'll be able to slot their adaptation to the Team USA roster accordingly in the overall evaluation. Me, I don't have the luxury of that much information. So from my armchair view of a couple TV games I'd say Shattenkirk and McDonagh (and Cole too) have impressed me and moved up my imaginary rankings. Cross would not be on my 1st round radar. For what little that's worth.