7.2 miles for me, plus .6 miles of parking lots so my commute is pretty similar.

I almost always do use "cycling clothes", but that's anything from the full roadie costume to cargo shorts with wicking t-shirt, and any combination. Sometimes slacks or even jeans. Given a short commute that most anything is OK, I have no standard for it.

The only "rules" I have for it is having a fresh shirt, or an option to change into one no matter what, and I don't wear slacks or dockers too often because the seats wear out.