Originally Posted by
e_guevara
This can be achieved on any bike, be it steel, aluminum, titanium, or CF.
Buy these are generally not, particularly on stock bikes. Additionally, shape and certain structural characteristics of carbon fiber frames are difficult to achieve with aluminum and steel. Keep in mind also that for some reason, top end aluminum bikes just aren't spec'd as well as carbon fiber bikes.
He didn't ask if he could upgrade all of his components, buy better wheels and tires, and commission a hydroformed aluminum frame, would that make him faster. He asked if someone having an aluminum framed bike, not cognizant of all of the details that make a bike and rider faster, could expect more speed if he bought a "nice carbon bike".
rpenmanparker's suggested testing method would work, is valid scientific method in my opinion, but wouldn't answer the question. If you really want to know the answer, take a number of representative bikes, put power meters on them, and run the tests. Or else ask the cyclists who have experience with upgrading from an aluminum bike, as OP did.