its actually kind of a tough question - depends on the day - the course - the goal - the group.....

Chilly Hilly yesterday - just over 16 mph in a group of about 6
My best time for a century (Apple Century Wenatchee WA) 4hrs 50 min ride time - drafting the hubby
Typical STP (Seattle to Portland Classic) pace - 15-17 mph
typical team training ride 14-15 mph average
Mt. Baker Hill climb (24.5 miles, 4300 feet) - just over 11 mph average- hope to make it at least 12 this year!