Originally Posted by
JohnDThompson
SLX has helical ribbing in crown end of the steer tube and the bottom bracket ends of the chainstays, seat and down tubes; SL only has the helical ribbing at the crown end of the steer tube. Supposedly, this makes SLX stiffer, although I've never been able to tell the difference. But I'm not the heaviest or most aggressive rider, so YMMV.
way way back when SLX arrived, the improvement for me was that it reduced distortion of the tube at brazed on front mech tabs, when those moved to investment cast bits that wrapped around the tube, the real reason to be was diminished.