Well done. Long commutes become a way of life after a while.
Dynamo drag: The dynamo in the winter makes almost no difference on my commutes. More important are wind, rain, temperature, wind, energy levels, number of clothing layers, time of week, wind, which bike I use, wind and, of course, wind....
I also have a back up battery light but rarely use it... (3W seriously bright torch with handlebar mount)
Don't skimp on dynamo light quality though. One of the new IQ's , Solidlights, or (drool, slobber) penury inducing Supernova E3....