Since CF bikes tend to be more expensive - I am assuming the bike shop is pushing those. Times are tough - they need to sell those CF bikes somehow.
CF can be as harsh as Alumnium - it can also be as soft and flexible as steel or Ti. Frankly why not then look at a steel or Ti bike? For the same price or less... you get a much more durable bike with the same nice road feel.
As for performance... it really is about you, not the bike. So many people look for the easy way out - "if I have the lightest bike I would ride faster" " if I have a more flexible bike I would ride father". Frankly if you just got out there and rode, you could do both.
Instead of buying the CF bike, opt for a carbon handlebar and fork. That will soften your ride, if that is a problem. As for doubling performance... that's all about you and your training and fitness.
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