As far as I know, SL4 Pro has a 42x68 alumin (non carbon) bb shell.
the sl4 frame has a 46x61mm frame. specialized's plastic cups bring the overall frame to 68mm...
The same forum (roadbikereview) has a lengthy discussion - educational, confusing or annoying - depending on your technical knowledge , seemed to conclude pressfit cups + adapter is not really a long term solution.
i can see how using specialized's plastic cups, without bearings, and then installing campy's 68x42 os-fit cups in that, is not a great idea. i feel there's too much potential for cup walk/pry-out. virenque
is talking about a different system entirely that uses specialized's plastic cups, with
bearings, then using specialized's new (available yet?) adapters which steps down the hole from 30mm to 24mm. this type of system has been used over and over, and is generally agreed to be the best way to go.
my only reservation is that specialized aluminum adapters can be creak-prone if not installed with very thick, very sticky grease. i prefer delrin, wheels manufacturing has something similar (you actually leave campy's bearings on the spindle, they will just be along for the ride) but is practically creak-free.
i dont like that the campy bearings dont get removed on that one, but hey, you cant have everything.