How big do your feeder and branch conductors really need to be? You may be undersizing conductors by using the ampacity tables in Art. 315, if you ignore 90.1(B) and the FPN in 315(A)(1). That FPN says the tables don't consider voltage drop. As noted in 90.1(B), following NEC requirements makes installations essentially free from hazard but not necessarily efficient.
Voltage drop is just one issue to consider when designing for efficiency. For example, if the loads have low power factor, high harmonics, and/or high wave distortion, they'll draw more current to do the same work. You can correct power factor and harmonics only so much before further correction is impractical. Thus, conductors will carry some “bad power.”
Article 315 tables are concerned with preventing conductors from melting. They aren't concerned with energy losses or with preventing insulation failure at 20% of normal conductor life.
Bigger conductors run cooler, but there is a limit to how big due to practical and price reasons. Rather than going to either extreme (NEC minimums or wastefully oversized conductors), perform an engineering analysis to determine the correct conductor sizes for each feeder and branch circuit.
