Yesterday on a calm day on a flat road I rode about 37 miles with the regular helmet (first chart), and today I rode 26 miles in high winds (18-20 mph) in the aero helmet on part of the same course. Both days I tried to keep the heart rate between 145 and 150. It's not an exact repeat of the ride, so it's not a great comparison, but FWIW:
Without aero helmet:
Average heart rate 144
Average speed: 16.1 mph
Maximum speed: 20.6 mph
With aero helmet:
Average heart rate 143
Average speed: 16.6 mph
Maximum speed: 21.9 mph
I'd call the aero helmet a success! Faster at a similar heart rate in tougher conditions works for me! If I see that kind of improvement on the 56-mile bike course at Eagleman in 2 weeks it will cut my time something like 6 to 8 minutes.
It was quite comfortable, too. It seemed to work especially well going into the wind where I felt I was able to maintain my speed better. I was also more conscious of my position and maintained it more steadily. I just have to get over feeling like a total dork poser when I'm wearing it.
I was just glad I didn't try putting on my new wheel cover yet, because I would have been blown all over the road.