I would add that when rehabbing a vintage bike, I notice performance improvement from hubs that have been cleaned, serviced with new bearings, and properly adjusted. It pays to have great hubs to begin with, but after they have been serviced, the efficiency of the bike improves a lot. During a Detroit Slow Roll, I find I don't need to pedal as much or fast to stay with the pace among hundreds of vintage bikes that clearly look neglected maintenance wise.

Tire pressure influences pedaling efficiency as well.