Can someone explain the difference of upgrading to the 105? I'm looking at the Ruby Sport Compact. My LBS offers rentals, so I'm planning on taking a Ruby for a spin, but I'm not exactly sure which models they have for rental. It would be helpful to know what to look for (beyond good fit). I'm new to road bikes - well "new" in the sense that I haven't owned or ridden one for about 25 years. I don't want to get all excited and buy what they have in stock, not understanding the detail differences between the models.