This is great information. At the conceptual level, I realize I was thinking in PSI but really should have been thinking in terms of volumes.
From a tactical perspective, it looks I can get about 3.74 volumes by setting a spundling valve on the keg to 44.6 PSI. My logic is this:
At serving temp of 46F, 3.74 volumes gives 30PSI, well within the range of our champagne bottles rated up to 90 PSI. Of course, the bottle might sit at room temp for a while and maybe even get too hot if I give it to someone that doesn't take care. However, using this calculator (https://hopsteiner.us/psi-calculator/) 3.74 volumes at 80F is still only 56.7 PSI, still well within the bottle range.
Assuming the keg sits at 65 degrees (a cool great lakes basement), using the same calculator says 3.74 volumes gives 44.6 PSI, within the range of even a 60PSI corny keg (even though I think I will have access to Corny kegs rated to 130PSI).
Even without a spundling valve, my guess is there is a sugar->volumes calculator somewhere that I could use to hit the 3.74 volumes and associated PSI limits.
This has been super helpful.
