I saw the opening post before anyone commented and decided to wait and see what others had to say - interesting.

I have done aero testing sessions but the best one to date was at the Velo Sports Center run by ERO. DC RainMaker did a review of the service http://www.dcrainmaker.com/2013/05/a...is-system.html and if you scroll down, OP can get the answer to his question from the data. As one rides around the track, the CdA is calculated instantaneously and displayed on a laptop. All of the test runs are compiled and one can determine the best equipment and riding position combination.

My wife and I spent 3 hours each on the track doing runs so we have a significant database of what equipment and position on the bike works. Some of the results are obvious and others are subtle. Some ideas that we thought were clear wins turned out to be a marginal improvement or worse. The other aspect is I learned a lot and do not have to rely on information provided by others although manufacturers results and ideas are a good point of departure. My advice is to test and not just believe. New and better aero helmets may not actually be faster on YOU. YMMV