I have been riding my 1990 Serotta (56x55.5) and it has the SLX tubeset.

The geometry isn't really any "tighter" than my SL bikes, but I swear it has a pretty harsh (really stiff) feel. Granted it's geometry/tires/wheels/saddle etc. but it's the first lugged steel bike that has felt this way besides my steel track bikes. It's really noticeable.

I could have sworn that the word on the street of yesteryear was that SLX was for lighter riders, SL the standard, and SP for the big guys.

Anyway, the helical internal ribs on the SLX were designed for what end again?