They ride team trials on time trial bikes, not aero road bikes…
I guess if your main objective is fast solo riding, or you’re a sprinter, then maybe a venge would be the way to go. But I’d take the 25W with a pinch of salt – that is a lot, even as a percentage of pro wattage, and if that was the advantage under general conditions then surely all the specialized riders would be on one (Nibali, Contador, Kwiatkowski, Boonen, Roche, Terpstra etc.etc.). Most people on astana/OPQS/saxo-tinkoff (Cav excepted) seem to prefer the Tarmac, which always struck me as odd given the negligible weight difference and the purported advantage of the aero frame.
Nothing against aero bikes, I used to have an cervelo S2 and loved it, but I think the 25W thing must be at 42 kmh with a perfect headwind of 23 kmh only, or some other lab outlier, or everyone would be on the venge, surely?
Anyway, I’d get the supersix as it looks better.