In theory, it'd have to be the 180k reputation milestone.
At that point, you get 90 bonus flags for the maximum of 100 moderator flags each day, regardless of your flagging history. However, in practice this is (now) mostly meaningless because most of your bonus flags will come from your flags that were deemed helpfulflags that were deemed helpful anyway, and you can get to 100 flags with just 15 rep.
Maxing out your delete votes however is based only on your reputation and happens a lot sooner than that: 30 votes at 35k reputation.