G1/G7 ballistic coefficient diffrences

[mapper]

So,
To do a table right,
If a person had a list of g7 bc's at diffrent velocities, would they take an average of them, or use the one at the velocity/longest range they intend to shoot, providing the velocity is still supersonic,( mach 1.2 I think I saw somewhere) then verify by shots on targets at known ranges? Or put whatever bc is given either g1 or g7, and a measured muzzle velocity, and adjust from there, or are the diffrences not enough to be concerned with at NRA mid to long range distances...
I don't have anything capable of reaching farther than that..

Jbm ballistics has the g7 data in their library listed as (litz) otherwise it is g1 I think...
The bullet data base has some listed with velocities but does not make a distinction of which model it Is..

It may be a moot point with my shooting skills,or lack of, but I would like to know the proper way to derive a drop/driftc chart based on best available info..

Other wise I have been within reason and a couple clicks with a measured muzzle velocity, and a simple bc.. but that has been at short ranges