I'm fairly consistent I suppose...but that has only been once I started eating a little before leaving. I notice that too when I do Saturday morning rides...I just ride better after eating a little something. Though my speed commuting doesn't really bother me or matter to me. I'll be slow some days, faster other days...I just try to enjoy the ride. I know the parts where I have to dig down and push myself if I want to do better time wise, but really a few minutes is a few minutes. There isn't any real difference to me if it takes me 42 minutes vs 46 minutes.