About the frame, I may be incorrect here, but it seems like some people are assuming aero power savings are linearly additive.
For example, if a handlebar change saves 12W independently, and a frame change saves 8W, the change together might only save 15W, rather than 20. In this example, it doesn’t mean that the frame alone only saves 3W. I guess it depends on how you look at it. Watts/$ are another story. The handlebar is the clear winner there.
As with the SL8 specifically, a big reason I’m not getting one is the lack of long, narrow cockpits and the inability to customize that on a $14k bike. The relatively short, wide cockpits spec’d on the bikes more than negates the aero benefits or adds even more cost.