He made a couple of runs with the ball during the Russia game, where he pulled away from defenders. I think his wheels are better than people think, just doesn't show em off as much.
I watch a lot and I think he is a fantastic player. But he is not fast. But as I said below, he is SOCCER fast, which is far more important.
Mikes top end speed is fine (not great, but decent enough), its his quickness, particularly his lateral quickness, that causes him problems. Hes got a lot of wonderful qualities though. So you either have to be a little careful how you use him, or just realize that to play him your giving up some things defensively to get some offensive things and try to make sure the trade is worth it. Again, hes developed wonderfully, so it usually is, but its a mistake not to think the tradeoff is there. Against a weaker opponent he is fine as a 6, defense is less important then keeping possession and moving the ball around well. I think it gets a lot dicier when the opponent can attack him in space effectively. I wouldn't be surprised to see him used at this position against teams that don't look to really push out against Roma but sit back and try to pack it in.
I think Mike's full out sprint speed is more than fine, if you look at world cup top speed data he's in the top quarter of players. I'd think that his relative lack of quickness is an issue when he has to turn and run over 5-10 yards, if he's being attacked in space he likely has time to anticipate or the time to recover.