From one specific ride that fits your parameters. Data from Garmin Connect.

Average Speed solo: 18.5 mph
Average Cadence solo: avg 80, max 103
Average Cadence group: n/a
Average Speed group: n/a
Chain Ring sizes (eg. 50/36): 50/34
Cassette range (eg. 12-28): 11/28
Number of sprockets on cassette: 10
Age: 60

A couple extras data points

distance: 23.1 miles
elevation gain: 486'
avg temp: 88.6
heart rate: avg 147 - max 160
ride date: Fri. May 27, 2011
misc: no signals, two stop signs (traffic non-existent, so only slowed, didn't "stop"), stiff wind that day