ASW-20 flaps setting VS speed

Hi,
I was reading the Johnson's ASW-20 flight evaluation. He says the -6
degrees flap setting is useless and that 0 degree is better up to
76kts, where the -9 degrees should then be selected.
Johnson also says something about the possible -4 degrees flaps
setting that might be more useful than the -6.

- Do you guys feel that the -6 setting is useless?
- Have you drilled a new -4 flap position to replace the -6 and if so,
does it seem to work great?

Thx