Carbon frame, stiff, made for race situations. Geometry optimized for Aero position. Shape of tubes are fine tuned to reduce aerodynamic drag. Especially the head tube for integrated brake cables has very little frontal surface area. That is an artisan master piece - you will not find something similar with mass produced monocoque frames.

Shimano Ultegra Di2. Affordable, light weight, spares available. "The effective frontal surface area" is most important for good aerodynamic behavior. Shimano wins by far with its front and rear derailleur shape.

Deda Alanera, Superzero RS or Superbox. What feels better in your hands. What combination looks better. Which one is service friendly. Are there spare parts available, now and in near future, because the cockpit (with headset) is subject for wear and tear. I personally prefer the Superbox for my own road bicycle RACE. And for my test and rental bicycles, because the combination is service friendly.

Three things make your bicycle more than anything else aerodynamic. More handlebar drop and deep rim wheels. 

A Deda Vinci stem gives you about 1.5 cm more handlebar drop, with the same head tube length. Of course a shorter head tube is even better. 

Campagnolo Bora WTO 60 mm wheels with Vittoria Corsa Pro Speed Cotton tires. 

When cruising at high speeds the slow down by air drag will be minimized.

Admitted, that the lower handlebar drop is just an adjustment, the riders low head position is the great aerodynamic advantage. If he can handle that. Please be careful, on roads with traffic, with aerodynamic positions.