Originally Posted by purevl

Alright, if you say so. The Columbus tubing charts that I've seen indicate that the only difference between the two sets is the reinforcements, so I would assume that would be the way to tell. I don't pretend to have any interest in Italian bikes though, I just have one, and it's SLX, so I've done a bit of research on the tubing. Looking for the ridges seems to be a pretty widely accepted method of making the determination.

Originally Posted by Picchio Special

The "helical reinforcements" got their start as a modification to the SL set when braze-on front derailleurs came into vogue. The idea is that they dissipate the heat and help prevent cooking the tube when the derailleur tab was added. So some SL sets will have them. SLX was a marketing move to take advantage of the idea by expanding it to the whole set. You'd have to check more than just the seattube to determine if the frame was actually built with SLX. I'm guessing that the OP's frame is SL - I think it's too early for SLX, and Colnago seems to have moved away from the chrome lugs when they began to distinguish the Superissimo by tubing type.