I just bought a 2013 Synapse 5 105 and love it.
I tried the Roubaix, Sectuer, Madone 3.1 and Defy alu.
The fit and ride on the Synapse worked the best for me.
I thought long and hard about going carbon, but all the
roads are flat here, and the best rides locally, Suncoast and Flatwoods,
are smoothly paved, so I just couldn't justify the cost of carbon.
I am REALLY happy with the Synapse in alu, and just rode it last
night. Every time, it just feels like one of the best purchases that I've ever made.
I, also, had a 2005 Allez Elite, and it was nice, but the geo of the
Synapse is better for me. As you can see, all the models that I was
looking at were relaxed geometry. I think the CAAD 10's are sweet,
just not for my needs.
BTW, I'm 51 and just a cruiser (16-19 mph) roadie.
Good luck.

S.