i think you would need to be extremely fast to start seeing your speed effect attachment
If you google and start reading on commonly used naca shapes you can find wind tunnel data and detachment points in relation to Reynolds number
Human powered LSR bicycle guys have a lot of info on shapes around naca 0024 , and wind turbine blades are often at naca 0018 (this has a bit of info available )
on a APS bike your probably limited to a naca 0021 to a 0024 unless you dont mind a larger rear surface where you cut it off
In my experiance it seems difficult to get the air to reattach after the leg cutouts , it can take up to3 feet to stabilise the flow , which just gives you a broad area for the turbulance to act on if you get it wrong