There are three generations of framesets before the CAAD ones.

Original (I called them 5.0s after their perceived weight and the newer 3.0 and 2.8s). "SR" framesets.



3.0s. These were 3 pound framesets. Originally came with one size downtube (huge), later divided into huge downtubes ('crit frame') and thinner downtubes ('road race frame'). The big feature was the dropout that extended past the stays, a feature named "cantilever dropouts" which really didn't match what "cantilever" means. This was their first foray into thin seatstays.



2.8s. 2.8 lbs or less for a frame. Tapered downtube, combining the best of the 3.0 crit and road frames.



After that I was out of the biz and I don't know what really happened. The SystemSix downtube is closer to the 'crit' size, that's the next Cannondale I owned. The Six13 was more like the 'road' version of this frame, softer overall. The SystemSix, when I bought it, was their most efficient frame ever, according to an engineer there. He recommended it to me based on my preference for 1-2 hour long rides, although it was fine for 6-7 hour rides too.