I have the Synapse and I love it, but CA is right Cannondales are stiff. you may love this or not, I personally love it now that I have rode a bike that is not stiff. What are your goals with this bike? Mine is stiff but also built for a little more comfort (and carbon) while my husband has a R5000 (alum) pure race machine and some long rides can be a little more harsh for him. He doesn't mind but I would not enjoy 60+ milers on aluminum, it can be such a harsh ride. Of course I am comparing it to my lower end, poorer fitting aluminum commuter so it isn't apples to apples.

You can always put a carbon seat post and probably get a relatively supple ride even with the harsher ride of aluminum. And let me clarify nothing wrong with aluminum but it is different ride from steel, carbon, titanium. I am assuming at your price point (guessing by this bike) most things you are looking at will be aluminum.

Can he let you take it for a slightly longer ride? Maybe somewhere with rougher roads? Cannondales are fabulous bikes, good quality and I have heard they stand behind them for warranty issues if they arise so the bike itself would not be a bad investment, just make sure it is compatible with your goals.