If you want to ride fast you need to get a decent sub 25 lb bike, get a real crank and casette (e.g. 52-39 and 11-23/25), run high pressure skinnies (23-25 @ 110-130 psi), go clipless, and learn to spin. It also helps to have a healthy disrespect for minor car-centric traffic laws!
Commuter A: Orbea Diem, Ultegra drive train, 105 crank, Deore Hydro discs, wellgo spd pedals (326 g).
Commuter B: Trek 7.9 frame (free replacement for 7.5 FX), Ultegra-105 mix, 105 crank, Nashbar CF fork, Front BB7 disc, thomson Stem and Post, wellgo spd pedals (326 g).