I second Doge here. Most wind-tunnel tests involve holding an optimized position and further optimizing it.

In a real TT, the rider hits bumps, turns corners, hits side-winds, and moves his whole body and head. The gains which add up over a 40K test might be much smaller over an actual 40 K race.

As he notes, a lot of folks have moved away from the really long-tailed aero helmet because while it provides a tiny benefit when perfectly oriented, it provides excellent braking in any other orientation.

not saying don't do all the testing and don't buy all the gear. Half-a-percent can be the winning margin. And even if you don't race, buy what brings satisfaction, regardless of the numbers. But ... it is useful to know which numbers apply and how much, in the real world---unless you are a pro wind-tunnel test-rider.