I tend to ride at a 80% pace.
Why? Slow enough to keep fresh riding every day but fast enough to not have to wake up too early and to arrive home at time for gym.

12 miles each way, not big hills but some climbs, always descending or climbing a little. Bike is a Surly LHT, racks, etc, Continental Speed Rides 700x42 and a pair of panniers with 25lbs inside. I tend to average 16mph