I use it right off Strava.

I wouldn't get too wrapped up in it.

My average speeds tend to go up as much as 20% or more if I'm on a group ride, because I'm drafting much of the time a and trying not to be left behind.

Riding on my own I don't crank it unless I'm on a segment.

I do look at the hammerheads rides on the same terrain. My averages range from 11-14 MPH. Theirs goes from 17-20 MPH. These are cat 2 racers. When a recreational rider claims to be going faster than that, I take it with a grain of salt.

ex: This fellow took 15th in his age group at thr World CX competition here in Feb. He's also the famous Dr. John: http://app.strava.com/activities/52274364