You can't buy speed. It's in the legs. Fabian Cancellara could make your current (commuter) bike go faster than you could make his current (race) bike go. It's easier to go fast (providing you have the legs for it) if you don't push as many air molecules out of the way, so a bike that puts you in a more aerodynamic position will help you accomplish that goal. If you don't care about the amount of effort needed, and really want to be upright while riding, build up your legs (a lot) and keep your current bike.