Originally Posted by Masque

Saddle: Make sure a 143mm saddle is right for you. I do not understand how Specialized will sell you a $10k bike but insist you take the 143mm saddle width.

Tires: You're on the right track, in my humble opinion. I switched immediately to GP 4000 S II 28s when I got my Roubaix Expert UDi2; I rode on the Turbos for 20 test ride miles and found them to be just fine, but you can't beat those Conti's. The 28 fits with just a hair of clearance.

Stack height: Make sure your LBS knows how to alter the stack height, and that you get it set up right. If things are done in the wrong order, bad things can follow. (If you're so inclined, Specialized has a VERY fast-paced video on the topic: Technical Service Videos - 2017 Roubaix/Ruby Booster Spring Swap & SWAT Box Install on Vimeo )

FutureShock: As for the suspension, personally I found the yellow 40lb spring to be the best of them, and that is the spring which should be installed by default, but have them swap them out so you can try each one before you take it home.

Lastly, availability on the S-Works model seems problematic. The Pro model isn't much better. If you're lucky enough to find either, I'd jump on whichever you find.