Speed never plays a role in my commute unless I find myself riding home with friends that work and commute in the same area; things can get a little "racy" with them. I choose to ride a heavy, bomb proof bike that'll get me to my destination without worry, and it's always loaded with clothes and things. At 48 miles round trip, if I tried to go out and kill it on every ride, my legs would be shot, and I'd get sick of the grind really quick. Because of the distance I ride, I'm good for 2 days at a minimum, with a goal of 3 days per week. I sprinkle in mountain biking on my non-commute days to keep things exciting, and those are the days that I go out and bust a lung. I also make an honest attempt to be car light, so on my days off, I also grocery shop and run errands on my longtail. A speedy commute pace could potentially derail my entire week of enjoyable cycling. All that said, being buzzed by fellow cyclists while commuting can get my juices flowing....lol, but that's a whole different thread that's been done.....