[Cryptography] What is total world transaction volume?

[James A. Donald]

Bitcoin cannot replace government money because there is a soft limit on 
the number of transactions, and we are already hitting that limit.

Also because final settlement is a bit slow.

Gold cannot replace government money, because it is easier to transfer 
promises than physical gold, although we may well return to the gold 
standard after the next crisis or two.

What is the total number of credit and debit card transactions, 
including atm transactions, per unit time?

How many transactions would a crypto currency need to handle per unit 
time to replace government money?