I'm about to increase my daily commute from 5 km each way to 10 km each way. I've been using a MTB converted to a commuter for years. Given the extra distance, regular evening head wind, and aging body, I'm considering getting a road or cyclocross bike or for better efficiency.
I usually commute with a large backback full of clothes, towel, laptop, lunch containers, etc. My question is, would the aerodynamic gain of switching to a road bike be negated by the backback? If so, would panniers or some other solution be better in terms of drag?