If I was commuting that distance, I would definitely wear cycling clothing on my commute. Heck, I already do and my commute is a fraction of that distance. My work is at the top of a hill, and I'm a sweaty mess when I arrive, so wearing my work cloths on the way in is not an option. Cycling clothes/lycra will dry before the end of the day. I wear lycra shorts under a pair of athletic shorts, or MTB shorts with padding/liner. Typically I wear a t-shirt and a clean spare for the ride home, plus a jacket/shell on top if it's a cold morning (mild CA weather).