Jonathan, Chad and I flew down to LA earlier this year and visited Ero Sports for aero testing. We were trying to improve our aerodynamics for our TT that I failed miserably at .
As a rule of thumb, every .001 is a watt, so if you go from .241 to .240 you saved a watt.
As a point of reference world-class tour level TTers are around .200 - .220. Some very small people or people who adopt illegal UCI positions can get in the .18X area or even lower.
Note: Jonathan has a world-class CdA .
If you have any questions let us know!