Actually, I paid attention on the way home this evening, and I think the answer is "yes." Every time that I was on a flat or even a mild incline, and I looked down, I was going in excess of 20 MPH, and I am riding with a chest cold right now. There was no significant wind today. My average for the trip was 17.2, but that's because the last 40% of my ride is on gravel road, badly potholed and with constant up/down hills.

Typically I'd be going 22 on the flat, 20.x on a slight incline, drop to about 17 on bigger inclines, and down to the range for 12 to 14 for actual hills.

And I'm not really trying to go fast, I'm just clocking along at what seems comfortable and sustainable.