First: I like Matthews over Murray. Like others have said, it's too risky to start Murray after such a long absence because we have no idea how much the Cowboys will use him this week. He certainly could have a 15-20+ carry day and be a solid RB1, but it's just as likely that he gets 5-10 carries as they ease him back in. Matthews hasn't been great lately, but he's a safer play than Murray, for this week at least.
Second: I actually like Wells here. While Tomlin did name Dwyer the starter, there's still a decent chance he splits carries and it's rare that any RB has a great game in a Steelers/Ravens matchup. Beanie had a great game last week and I think he proved that he's healthy and capable of handling a big load. There's no promise that either of these have great (or even decent) games, but I think Beanie is the safer play.
Here's mine: viewtopic.php?f=19&t=530760