I have no idea, but a good start would probably to have P99 .40 owners post round counts and current condition of their P99's.
Looking at my log, my P99 .40 has got 1839 rounds through it and is still in excellent condition. No large amount of wear anywhere on the gun. You can see pics here
to view wear.
I know there are some folks on this forum who have far more rounds through their P99 .40's than I do, so hopefully they'll post in this thread too.