Apologies if I ranted out some there. I'm dealing with these things every day now, and I'm seeing what I'm seeing, and hearing peoples' troubles, and it all links back to what I was saying above. As to why corporations do what they do... they're not doing what they do for the betterment of humanity and you and me. Job one is about dollars, not just about making a living, but making a killing. We're on our own if we want to accomplish something, like have the thing we have work correctly or to the best of it's ability... and that's fine, because we're equipped with all that's necessary to easily do better than they do, hot rodding 101.
You're on the right track. Trust your senses about how the car acts and what it wants to work well. Annular boosters in general can use a smaller jet to accomplish what a down leg or straight leg booster can, especially way up top, wide open throttle and red line, because they are more sensitive to airflow and will deliver more fuel with the airflow signal. I don't know how much more sensitive to airflow than other booster designs the 4180's annular primary boosters are, but I happen to like their design... they won't be restricting flow as much as others do, they are big around and slender and not really much of a restriction in the venturi... Mike likes unhindered airflow very much, and so do engines.
Why would "they"? ... for a thinking, feeling, intelligent human being, there is no comprehending why. I think all sorts of things done at the time (and today) were experiments, pushed and fueled (pun intended) by one corporation (government) and it's agenda twisting the arms of other corporations (auto makers) behind their backs, telling them what to do, or else... and "they" abandoned all the sound research and findings and rules established over 100 years ago as to what is at or near perfection for provision of the amounts to administer of air:fuel for most efficient and powerful internal combustion... 'nuff said.
All stock, or mild? I would imagine your troubles when at part throttle to heavier throttle would be over if you upped the primary jet to #64 (#61 primary jets is lean in other similar sized carburetors, and I'd like to say that I don't think the 4180's annular boosters are shining so much at lower air flows as some might think they do, hence the lean protest/sluggishness at part throttle to heavier throttle application), and installed an 8.5 PV. Reusing an older PV might not be a good idea, because even if still sealing manifold vacuum from pulling fuel through straight into the intake manifold, where it's not supposed to go, the diaphragms can get stiff over time, affecting the spring rate, especially with what we have now "they" call gasoline. Power valve number really is kind of arbitrary, but solely about full enrichment later with more/full load and wide(r) open throttle. Even if you installed a number PV that's the same as idle vacuum, it would make no difference, because if the main circuit is not flowing there is no affect on the idle/transition circuit. As you have correctly observed and stated/asked about, the only place the primary jetting and PV are of relevance is when you start putting your foot into the throttle harder. Point blank, getting the heavy load and WOT fuel mixture right, or close, or compromised and safe rich (the corporate choice), is easy, the numbers of those components, like jets and power valves, are stamped right on them and basically not super important when discussing maximum fuel efficiency and happy engine function in most "normal" driving... that's the department of the idle and transition circuit, where truly surprising levels of function and fuel efficiency can be had, and we can get fully into that deeper if you wish with your thread.
The two-stage is "robbing from Peter to pay Paul", and IMHO, just another thing among other super secret and scientifically calibrated sensitive equipment that simply ends up getting in the way of basic, good, best function.
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