This subject has been beat to death on Moparts many times before; the idle vacuum shouldn't have any impact on the selection of the power valve because the power circuit should not see any vacuum at idle. If the power circuit is seeing vacuum at idle then something is wrong and needs addressed. At least in most cases.

I agree with the position that the cruise vacuum is much more important when choosing the opening point for the power valve. I often use 9.5 or 10.5 power valves. Our engines are not near as picky about an early opening PV as they are about a late opening one. Late opening PVs can cause all kinds of driving problems, while early opening ones rarely, if ever, cause any.

And while I am sure that all the suggestions here are well intentioned, many of them are frankly not something that the OP probably should be attempting until he has more experience modifying carbs.