Power Valve Selection: The Definitive Answer

There are varying opinions on how one goes about selecting a power valve for Holley based carbs (as anyone who has worked on one well knows) There's the 1/2 of idle vacuum, either with 4-speed in neutral or auto in drive, the more widely accepted 2" less than cruise vacuum, I've also seen people mentioning 1/2 of cruise vacuum, some say split the idle and cruise vacuum reading and 1/2 it, and other ways not widely accepted or worth considering. With the highly regarded knowledge base here, as well as referencing David Vizards Holley tuning book, and just focusing on the 2" less than cruise vacuum theory, all the while keeping in mind it is a way to establish a baseline or ball park selection in order to further fine tune: So I'm using the 2" less than cruise method on my AED 750 dp with an as furnished 4.5" PV (it just so happens I have a best idle in gear vacuum reading of 9", so the current PV is in line with the 1/2 theory) but anyway, all other tuning aside, assuming the other carb circuits are close, timing etc are close with current carb jetting, and you have let's say 17" (and sometimes close to 20"+/- in some instances) cruise on primaries, 50-70 mph, 2000-3000 rpm just as a rough example. I'd be looking at a 15" PV, but as we know they don't make one, so the highest is the difficult to find 12.5", or the readily available 10.5". So I could just slap that in and get to further tuning, or slap a plug in and do afr and vacuum readings to hone in on the ideal PV selection, selecting one that opens in relation to the lean reading and vacuum reading.... but how much above or as close to that point? Hope that makes sense. Who has done the plug method taking readings to identify the going lean point in order to determine ideal PV opening? And for those using the 2" below cruise method, using the closest PV, did you have to make any more valve changes down? And would there really be much difference between 8.5"-10.5" with such high cruise vacuum of 17"? Is it the choice between being lazy and taking any and all time? I'm feeling really lazy right now!! :rolleyes: