Solo: 16-18 MPH (depending on distance and elevation)
Monday group: 15-16 MPH
Weekend groups and endurance group: 13-15 MPH
Commutes: 11-14 MPH
The local A group tends to average 20-22 MPH. The B group seems a bit unfriendly to unknown women (hi) and sometimes turns into the A group. So, as it turns out, my solo rides are the fastest, at least until I can find (or create) a genuine B/C group with skilled riders who are not interested in rising through the ranks of the racing world.