The S5 puts an emphasis on aerodynamic performance and stiffness, making it a preferred base for the world's fastest sprinters. But don't believe that that's all - despite the lateral stiffness, the S5 is incredibly comfortable to ride. No doubt you've noticed the now legendary V-stem. Cervélo tweaked this shape to give the best possible wind performance, hide the cables inside, and make enough bar / stem / stack options to fit pretty much everyone.
When you step on an S5, not only will you go fast, but you'll feel fast too. The frame's stiffness, geometry, build, and tube shapes all combine to create a bike that's comfortable enough to be on the road all day but is more responsive to last-minute acceleration than anything else. It's suitable for 28mm tires so you can fit the newer, wider rim / tire combinations that will help you get an even bigger aero advantage.