Stiffness of the frame is only uncomfortable on bad roads but it's doubtful the S-Works frame will be much stiffer than the regular Roubaix. How much weight difference are you talking? Probably not much in the frame itself.
I am against buying used bikes, except vintage stuff and super cheap stuff. It could work out if you know exactly what you want and get some kind of warranty.
Last edited by big john; 02-04-21 at 10:38 AM.