Are carbon rails worth it?
Riding the track, you are more likely to break rails than on the road. I've seen averaged-sized racers both crack the saddle frame or break rails when hitting bumps on tracks.
I'd go for steel or "Kium" (whatever that is that Fizik uses) over titanium or carbon rails, even if I were of average weight.
I think carbon rails are simply for the weight weenie crowd and a way for companies to charge double for the same saddle.