How many sales copies do you make for a digital product?

[RuskinF]

If I am right, it means you are talking about A/B testing.
In this case, you should begin with two vastly different copies first.
Then select the one that works best.
Make two copies from the selected copy and alter it in two different ways.
See which one performs better and use that one.

Lather, Rinse, and Repeat this process until you find a practically-ideal copy.