Your estimates are fine, here is my ScanmyTesla report after a long drive. I've done 36k miles, rarely SC, most of the time car is charged to 60%.
Including the 4kWh buffer my car reports a nominal capacity of 67.7kWh, so rough 5% degredation if you assume 71.2kWh when new.
Including the 4kWh buffer my car reports a nominal capacity of 67.7kWh, so rough 5% degredation if you assume 71.2kWh when new.