The thing about Sillinger is that he only produces points when he's getting 18-20 minutes of icetime as a top-6 forward. And even then he only scores in the 45 point range, which isn't really going to cut it for a smallish #2 center. This is why he's moved around so much over the course of his career - he's a good stopgap, but as long as he's in your top 6, you're looking to upgrade and find someone better. As soon as he gets third-line icetime with third-line players, his production disappears - 14 points last year in 60 games with Phoenix, and a similar lack of production in TB, Philly and here when he wasn't getting prime minutes and PP time. And I don't really like him as a #3 center- he's too small to match up against most of the bigger elite centers in the league, doesn't provide much in the way of physical play, and isn't the fastest guy in the world either.
Yeah, he's good on faceoffs. But to me faceoffs have always been the most over-rated stat in the league. 95% of the centers in the league are between about 47% and 53%. A guy who wins 56% or 58% is winning one extra faceoff every two or so games, and I don't find that to be a huge deal.
Yes, he played well in St. Louis. But again, he was only scoring when he was getting 20 minutes of icetime/game, quality wingers, and loads of PP time, none of which he would get here. He's always been able to do a decent job for short spurts like that, but over the long haul he's not a legit top-6 guy on a quality team.
The thing with Sillinger is that he's never really been a 3rd-line center, and never been used in a defensive role. He's spent his whole career as a scoring-line center on crappy teams. That's what he was in Columbus, that's what he was in Florida, that's what he was in TB, that's what he was in Philly when they picked him up because of the Lindros injury, that's what he was here, and that's what he was in Anaheim. The only times in his career he's been used as a checking line center were last year in Phoenix, part of a season in TB, and part of a season in Philly. And each time he sucked. Just winning faceoffs doesn't make you a quality third-line center.
To get a read on what his impact would be here, look at what he did in Phoenix when he was playing the same role he would here, not what he did in St. Louis playing a completely different role.