Although I can not answer your question specifically, I have observed that the rate of throat erosion is HIGHLY dependant on the number of consecutive rounds fired, or in other words, internal metal temperature.
I have toasted small/medium bore barrels but ignoring the barrel temperature. Didn't have the time or patients to allow the barrel to cool COMPLETELY.
Conversely, I have two overbored cartridge guns that I NEVER shoot hot and always allow to fully cool (yes, its a pain in the neck sometimes). Both of them have exceeded the normal expected throat life and still shoot exceptionally well.
Heat kills throats.
VH