Visa says they process "150 million transactions every day in 175 currencies" (see page 3 at https://usa.visa.com/dam/VCOM/download/corporate/media/visan...). That's ~1,800 per second. Mastercard is smaller, so this would be the upper limit for them. Both combined should still fit into "a few thousand transactions per second".
True. The latest financial report from Visa [1] says 164.7B transactions in 2021, or ~5,000 per second. This number is 3x larger! Mastercard is slightly smaller, but comparable at 140B [2].
Visa says they process "150 million transactions every day in 175 currencies" (see page 3 at https://usa.visa.com/dam/VCOM/download/corporate/media/visan...). That's ~1,800 per second. Mastercard is smaller, so this would be the upper limit for them. Both combined should still fit into "a few thousand transactions per second".