I didn't have time today to do any serious testing or research; I will continue to report data as I collect more.
However, I did buy 8 cans at the local store suspecting we'd be learning as we went. I vacuumed out the system and began a slow recharge cycle as
@L31MaxExpress described. Lo and behold, after very small bursts and temp checking, right at exactly 3.5 cans seemed to be a sweet spot.
Delta hit the best it has ever been today on the highway with a low of 60° center vent from ambient of 100°F, recirc off. With rear blowers off, I gained 2-3 more degrees of cooling for the front.
Recirc door is definitely in need of inspection for seals since I only gain about an extra 5 degrees of cooling with it on. I'm sure if that gets sorted, my performance would be on par with what we expect from this system.
I had no idea how sensitive these systems were - that even a small amount of over charge of 4-5oz would yield a definitive decrease in performance. Thank you for taking the time to lay out the conversion and the dynamics of an overcharged system, it helped me understand what the gauges are telling me to a much deeper level.
The story isn't over, but I'm happy with the progress that's been made. Recirc seals, an e fan up front, and blower removal to check the seals is coming up next.