I took the carbon Synapse with hydraulic disc for a 10-mile test ride and then immediately took the aluminum 105 with mechanical disc for a ride. The difference I noticed between the two bikes was the brakes - the hydraulic was either on or off while the mechanical could be feathered. I am still a rookie so I may not have noticed all the finer details but that was my initial opinion. In the end, I was going to get the aluminum/mechanical disc as the carbon wasn't worth the additional $1K. However, I found a gem in a gently used bike right before I pulled the trigger.