I am comparing two different year bikes and the differences between them. The bike in question is the Trek 2.1. double compact. The `09 has carbon seatstays with 105 rederailur and Tiarga shifters while the `10 has complete 105 components with a normal frame. The price difference is about $150-200 more for the 105 group. So the question is; are the 105 components worth an addional $200 or is the carbon seatstays a worthwhile addition?

I tried searching but to search with the name "Trek" doesnt exactly narrow the field much.