if you don't plan on racing then get the bike that you feel most comfortable with. I am a caad 9-5 owner but would have no problem ridig that synapse and looked long and hard at it before I ended on the caad. would like to do some local crit races next year once I get into shape and feel comfortable riding in groups.
One note however when I got my caad t was set up pretty upright with the stem turned up and a number of spacers. It didn't have a very different feel from the synapse so, go try a caad for the hell of it but get the synapse if you like it and feel its the right bike for you.
BTW the liquidgas professional team have ridden and the synapse in the paris roubaix a tough coble stone climbing race, very much performance in this bike.