FINALLY! You are good IMO. Reason for non mid 40s or high 30'sF vent temps is return air is just not cool enough and wont be in such a large area. Like driving with windows open it's maxed out BTUs possible.
I need a week to write a comprehensive way to know you have reached the magic charge amount to behave the best at assorted temps and conditions. For laughs have done my own just because almost gram by gram up and down, drive around block and check all again for hours to achieve that.
OK - I think on a cooler day in general and moving along for some time unknown but not right away you'll really see that drop to the mid 40sF center vent the way it is now.
Watch engine temps if possible I think this has a gauge? Not accuracy so much as steady, all the time - no creeping up at a stop light, stop sign or in traffic. May not cool as well but engine must stay stable. If now stressed with warmer condenser it can radiate heat more than your radiator/engine heat added can do. This isn't hot for a layout like this just warning that you cooling system isn't up to par and should know it.
How many RPM will count driving or for sure sitting still. No surprise about it, compressor isn't turning as fast so normal,
Good luck. Don't go get greedy and add more but rather observe as much as possible day by day how it performs if there's more that should be considered otherwise be happy - that's about what I'd expect of this,