I usually ride at what I consider a moderate pace, about 15 mph. I learned pretty quickly that I got burned out from commuting if I tried to ride hard every day. However, you (the OP) are probably a lot younger than me, and your commute might be shorter. I'm 61, and my commute distance is 31 miles round trip. Sometimes I'll push the pace and ride a lot faster, but that usually means my legs will be tired the next commute.