Enves are known for excellent crosswind handling, thus I’d go for the 7.8s.
I believe @Nate_Pearson has mentioned wanting to try 7.8s after seeing @Pete and the Clif Bar team run them.
The main drawback is weight. I think the improvement in aerodynamics is worth the penalty. Hambini, like him or not, has mentioned that there’s a general consensus among aerodynamicists that for 28mm tires, you’ll want those 70-80mm rims, and IMO, 28mm tubeless is where it’s at right now.
As for sales, Enve did a $600 off trade in program over the holidays, but no direct sales on the disc wheels. Some places were selling the rim brake versions at half off, but the disc wheels were at full msrp.