And to not just take my word for it...go out on read some reviews of both the SL3 and SL4 Roubaix. Reviews are very different. Specialized changed every tube section on the SL4 when I thought the SL3 was nearly optimized. The result is a harsher bike which makes many scratch their heads because an uber stiff bike and endurance geometry don't seem or at least need to be compatible. The SL3 Roubaix is already a stiff bike and in fact, I was pretty surprised how stiff it was once I got it on the road. The SL2 Roubaix is a noodle compared to the SL3 which was a total redesign.

And a good point about how they are marketed. In some ways the Emonda is watershed because it is smack in between a pure race bike like Madone and Tarmac and an endurance geometry. If you study the geometry you will find this to be true in wheelbase, HT angle, head tube to top tube ratio etc. I like the Emonda a lot. The thing that sways me in favor of Specialized is I prefer BB30 to Trek's wider bottom bracket which can't be converted to English threaded for running either Campy or Shimano's cranks with less issue and I am not a fan of the seat mast design which is proprietary and relegates an owner to a single bolt seat post which I consider inferior to a solid 2 bolt. The Roubaix (and Tarmac) will both fit a generic 27.2 dia seat post.