I like the BMC bike but I have question why the miss-matched parts. Why is the front derailleur Dura Ace and the brakes? Just sounds weird. I am also leery of buying a used carbon fiber bike. Unless it is from someone you know, who can vouch for the integrity of the frame, I just wouldn't do it. You don't say if the Caad 12 is new or not but I would go for that one if it is.