> Multi-threading is a must, when scraping at scale. The more concurrent requests your spiders can make the better your performance - simple.

Intuitively I would think that this sort of problem would profit from using asynchronous ingestion at the edge pushing unprocessed contents to a multi-threaded/multi-process backend. (Because I'd expect that network latencies mean you need lots of threads to saturate I/O, which I'd expect would conflict with effectively using the available CPU power to do the actual document processing).