Im getting my first road bike and I've setteled on two road bikes (Both used). One is a full carbon Tiagra 4600 Groupset bike with Fulcrum quattro racing while the other is a carbon fork mixed groupset (Shifters: 105 5700, Crank 10S, BB: Dura-Ace, Rear Derailleur: Tiagra, Front Derailleur: Ultegra 6600, Casette: Dura-Ace, Chain: 105.Wheels: Fulcrum Racing 7. Mileage less then 1000km). The full carbon is slightly more expensive when compared to the carbon fork
I assume that because you said carbon fork with respect to the mixed group bike, that it's an aluminum frame? If so, if they're close in price, go with the full carbon 10 speed Tiagra. 4600 is not your father's Tiagra. It's not bad. Plus, the other bike has a Tiagra RD anyway.
The mixed of components on the other bike would indicate to me either a home built frankenbike, or one a shop put together out of spare parts.
