I rode the bike at the fitness center for fifteen minutes in Zone 2. I averaged 15 mph, 92 rpm and 131 bpm using gear 6. I weighed in at about 130 pounds.
Right now I can say that riding the stationary bike is harder (both physically and mentally) for me than riding my bike outdoors. I'll keep an eye on how or whether this changes as I do more workouts on the stationary bike and as the workout grow longer.
(As usual, I did use my bike for the method of transportation to and from the fitness center)