I think average speed is generally fine if you're doing a loop so net elevation change is 0. As you go up an incline slowly it takes a while, but descending will make up for speed. I notice my average speed is usually around 17mph no matter if I do a flat ride or a hilly ride. Headwinds are a big issue if the wind direction changes during the ride. I did a loop and the wind stayed the same, so at 180 watts one way I was going 14mph but on the way back I was doing 23mph with the same effort. Again, around 17 or 18mph average.