If you're looking at Tiagra, and still would like a carbon frame, take a look at one of the Fezzari Empire models (Empire Sport). 105? Look at the Comp.
Empire – Fezzari Bicycles
I own a Fezzari, and love it. You'd have a hard time finding a carbon bike for that price. In fact, the Empire Sport sells for less than their ultralight carbon frameset! Oh, and it comes with 28 spoke wheels.