If you are asking this question because you want to train better for racing, then the answer is to stay as close to your race setup as possible. For example, I had a carbon cervelo when I rode fulltime for racing, but I rode a alu cervelo with the exact same setup as my carbon bike. That way your body become trained not only from a fitness/cardio point of view, but it also becomes trained against fatigue, road harshness, etc. I would therefore recommend that you either train on your race rig (cause carbon doesnt really "get old") or buy a more entry level frame of the same make to train on (alu or carbon) and set it up with the same saddle, stem, handlebar and pedal system. That would be the best for training to get you ready for your racing. If its not for racing, then train on whatever makes you feel good!!!