I've seen the numbers, and I largely agree with them--in terms of their difference between positions. However, I don't think the CF number for either seems accurate. I would be willing to bet, after having watched nearly every red sox game for the past 4-5 years, that Crisp and Pena are AT LEAST equal in CF and over the long run I'm betting that Coco chases down and catches more balls than Pena. Pena often looks very uncomfortable out there.
I would be interested to see how he does in LF. In any case, I don't think there's ANY doubt about Ellsbury's skills as a CFer.
EDIT: before anyone is a smart ass, I realize the Sox haven't had Coco and Pena for 4-5 years. I was simply implying that, while stats count happenings in a game, they are used because most scouts don't watch every game to get a better idea of who the player is. That's all.