I can’t find any information on the aerodynamics of either the S3 or new S5, e.g. how they compare to each other mostly. Or the S3D (which I’m not considering, but Cervelo says it’s more aero than the S3 (S3R?), so I’m curious.
I recall Damon saying 4w for the S5 over the S3. I’d expect some of that is cable routing, so if you have Di2 on an S3 the impact will be reduced.
I went from AR to S5 (both 58), S5 feels a bit more solid.
Have also ridden the S3 and couldn’t fault that either, but S5 fit better.
In the end the fit aspect and the smug knowledge of having the best was enough to justify the extra cost of the S5 for me.