It really depends. For the most part, the answer is yes. Some will say that these new aero bikes like the Cervelo S5 and the Felt AR series are not good for long rides, but I don't really see why. A bike is a stiff, rigid structure regardless of how a bike company spins the marketing. Even the "vertically compliant" cobbles bikes like the Cervelo R3/5 and the Specialized Roubaix are stiff race bikes at heart. If you can do a century on a Cervelo R3 you can certainly do a century on the aero S5. The fit and choice of wheels are going to impact the ride quality more than the frame design.