Also, that "2 billion requests per day" might sound silly to someone who serves that in an hour...
Your sub-150ms invalidation is equally if not more impressive, especially if you're talking about multi-region invalidation.
As for the purging stuff, I do mean cross-region. So, it depends upon which node receives your purge request. 150ms is average, but really it's "network latency plus a millisecond or so".