i think the BD can be very good on carpet, Billy Easton did very well recently, but i think the BD is best on rubber tyres on carpet. How do you mean, graphite? The wishbones, hubs etc were not graphite as standard on my BD, but all the components are top quality. As previously stated the BD isnt really designed for foam carpet racing, thats probly why it doesnt come with the really hard graphite wishbones etc etc.
i think my BD is great, and rocks with rubber tyres on asphalt and carpet, but the desiion is yours. And a TC4 for a BD is a very good trade i think.