Good descending bikes have good, well balanced geometry and weight is non-relevant. I haven't ridden the Cervelos so I can't comment, though in smaller sizes their geometry is odd. The three best descending bikes I have ever ridden: Merckx Team Sc; Serotta (lugged steel ... blanking on the model right now); Colnago Dream. All of these bikes are/were scary fast downhill ... much much faster than I am capable of riding. The Merckx (my current bike) is so fast down hill it can get me in trouble before I realize it on some of the front range descents. I'd stick with something with traditional Euro geometry with a stiff toptube.

I've ridden several bikes that were scary on fast downhills ... Raleigh Technium (the 753 bike, Raleigh's top of the line bike at the time; Tomac won the US crit championship on it); terrifying highspeed shimmy, almost unrideable going downhill. Cannondale CAAD somethingorother; horrible horrible. GT road bike; horrible downhill, and bad everywhere else. And several others I can't think of right now. I think the common factor was a flexy toptube that couldn't keep the front end in line with the rear end.

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"In case of flood climb to safety"