My commute was 5.2 miles (8.3 km) one-way, and I usually rode my mountain bike rather than my road bike because it was easier to carry things, the roads were pretty rough in places, lots of glass from the liquor industry's success stories, etc.

I would average 10.5 miles per hour consistently, and 11.5 miles per hour on days when I got real sweaty.

The route had some short fairly steep hills, but was generally what you'd call flat.

So--I'm no speed demon. I find the concept of "perceived exertion," which I first read about in Runner's World magazine, very useful, and as a result I don't pay much mind to speed, just to how I feel during and after a ride. Speed, as far as I'm concerned, is for racers.

I would also regularly measure my pulse and blood pressure at home, (I have an inherited tendency to high blood pressure) and was generally mightily pleased!