So what are all of the factors?
1. The linear speed of the chain speed
2. The amount each link must rotate
3. Aerodynamic drag
4. The flywheel effect
5. Total weight
6. What else?
IMHO, since the highly unusual 63-19 and 40-12 are equivalent options to the popular 47-14 & 50-15, that maybe the sweet spot lies in that 14-15t cog range and that significant differences might only be felt at the extremes.