The tx/sec are guesses. Its too soon to know what the upper limits of blockchain TPS could be.

The arguments for massive TPS scaling are not that the Ethereum base chain itself will process them at transaction time, but that that L2+ chains will process transactions and settle on the ETH base chain, similar to what the ACH does.

The two scaling concepts to watch for are rollups (transaction batches that are rolled up into a single state change), and sharding (similar to database sharding.)

Here is a nice viewer for current TPS https://ethtps.info/

When requesting a “citation” I would recommend you provide the what bounds and types of information is acceptable to you.