I'm not an engineer nor do I play one in real or any make believe life. The air after hitting the front of a softride is able to reform into smoother layers than a double diamond frame. You get smoother air hitting your back wheel w/ the softride vs the frame downtube churning the air. I would argue that the softride would be a faster frame than the standard double diamond frame no matter what back wheel you toss on. edit:
I don't think the frame, no matter what it's style, makes as much difference as rider position.
Brian Stover Accelerate3 Coaching
twitter & IG = @accelerate3