I do wear work clothes (hence why I'm sweating when I arrive. I can ride for two hours in bike shorts and Under Armour and not break a sweat). The slow pace is another issue altogether. I push myself pretty hard when I bike in traffic, I guess I feel obligated to go as fast as I can to avoid affecting traffic. I also think I am probably safer with a smaller speed differential between myself and the cars (more time for them to see me). But you're right I could probably bike in at 8mph and not break a sweat.