Actually, most people are COMPLETELY WRONG about the drivetrain losses. Today's $600 drivetrain can be built ONLY because they are using high-friction sealed bearings in the hubs and the bottom bracket, and usually, in the headset and pedals. The cup-and-cone stuff from the 70's has lower friction when properly adjusted (even vs. ceramic sealed bearings.) So there is reason to believe that if you don't miss a shift, you will be FASTER on a vintage bike, especially on the flats.
However, as we all know, aerodynamics has the greatest impact on performance above 20 mph, and in that area there has been little progress as much of the losses are from the rider, not from the bike. We'll have to wait for evolution to make improvements there.
The one area where aerodynamic improvements are possible is in the wheels, however, excluding monocoque wheels, I'd be surprised if today's wheels are measurably better than retro 28h wheels.
- Don Gillies
San Diego, CA, USA