If you look at history, when it was clear BSA needed improvement from an engineering perspective, people came up with outboard BB cups -- a half asset approach, which pushed cranks further out. Cranks became thinner laterally coz bearing cups do not leave much space for crank arms.

For example, current campy crank arms are much flatter than the square tapered version, and you have to over build the cranks to achieve the desired stiffness. That's why a whole frame is 700-1100g, and a friggin crankset has to be 600-800g.

Too much emphasis is placed on the frame, hence it gets lighter and lighter with wall thickness of around 1.5mm. But carbon cranks have much thicker walls. BBright and BB386 widens the BB shell to the max, while it's the poor old crank arms that take the most load much more directly coming from the pedals. In other words, the frame "cheated" for more (and unnecessary) width, as a result of the outboard bearing movement. Poor cranks are stuck with no room to be optimized. This is true for BB386, BB86, and BBright.

Not to mention ankle clearance and Q factor. This is unfortunate, because the industry is less integrated, and Cervelo/BH/Wilier don't know how to make a super lightweight stiff crank with thin walls. Exactly why Cannondale is so superior in this area.

here's the easy answer.
the fsa bb30-to-english adapter doesnt fit the SL4. SL4 is 46mm ID, like PF30 (but not). the fsa adapter only works on 42mm bb30 frames.
the adapters that come with specialized frames (that are NOT wheelsmfg adapters) are slightly loose fitting, and have been known to creak. i used a super-heavy, super-tacky grease on the latest one, we'll see how that goes.
the best option is actually wheelsmfg adapters, they are delrin, a slightly more snug fit, and wont creak.

Praxis Works?

BB30 Conversion Kit: http://praxiscycles.com/pages/bb30-conversion

Video: http://praxiscycles.com/videos/conversion_install.mp4