Air/ fuel tuning

How did you determine you need a 6.5 power valve? I have ~ 10 inches of idle vacuum and I'm using a 10.5 PV and may need to go to a 12.5. Seems to me unless you have very little cruise vacuum you still need an earlier opening PV.
ROSE! I can`t believe u said that ! Forever the word on power valves , have been "half" of ur vacuum . I didn`t read all the posts, because I have a timing controlled fuel .inj. set up, but do read some to see what others are doing , regarding mixtures. Maybe I missed something .?????