I am not arguing cfm requirements, although later in this post, I do argue carb sizing using maximum calculated cfm requirements a bit. What I am saying the 500 Edelbrock is a weak 500. Look down inside one from the choke, it's an airflow mess, the 600 Edelbrock is different and will not have any negative effect on that engine.
This is not the standard "who picks the right size carb" argument, that Edel 500 is a lose-lose because it is very turbulent and hard to keep a stable mixture through the curve and can be more expensive. So, again, I am not pushing for a bigger carb for her car, the way she drives it, just pushing back on an Edel 500 only.
However, too big of a carb hurts nobody as long as the boosters have an adequate signal to come on line when needed . A carb venturi is not a intake port or plenum, the velocity in each venturi only matters as it relates to the booster and the signal it "feels" in the circuit. Thats why some BIG carbs with annual boosters are very tunable at low rpm and at the same time will go pig rich at high rpm. Also why some small carbs need a bunch of enrichment to get on the mains (Street Avenger series and early HP Holleys). As long the mains can come on line with good atomized fuel when they need to, which is a function of booster, bleed, and emulsion design along with venturi size and shape, a carb "too big" for the application runs very well. Remember a clean venturi could flow more but have better velocity and signal to the booster just because it is more efficient, that's what I am saying is happening with the 600 vs the 500 Edel.
I am very leery of comparing that to an intake port though, it is very different. Port cross section, length, plenum volume, all very significant on torque and HP curve, but working back from the valve, once those pulses are minimized in the plenum, what you are describing doesn't apply to the carb. The key job for a carb is just to manage a/f during transition from circuit to circuit and account for load with some enrichment circuit, it is not an extension of the intake port, unless it's an individual runner manifold
Now, I agree that the engine will only pull the air it can mechanically pull, excluding things like overlap, negative exhaust pulses, intake resonance benefits, etc, and her stock FE it's never going to need more than 450 cfm or so. However, for the crowd, a set of properly sized headers, a tighter LSA, and good clean intake port, that same cid and RPM range can pull harder on a carb, (none of which is applicable on her stock 390) so I am a bit leery of going small on engines that are optimized for an RPM range, even if that RPM is low, and without a dyno sheet, even a mild FE can be wanting more. I know you addressed it with BFSC, but without testing the engine, that CFM calculation is immediately based on an assumption (even though I agree that the number is likely right)
However, 600 cfm is not big for a 390, Ford used a 600 Holley on 390GTs, and they used a horrible intake manifold and exhaust manifold design that negated a bit more cam, of course the 4100s and 4300s were sized small on the rest of them, but my point is just that the range from 450-600 is all very usable in a lo-po 390 as demonstrated in countless Edel 600s and 1850 Holleys being used every day.