I'll say this - they can do some impressive transactions per second (they hover around 2000/sec) and can burst to 40,000/sec, but they can't sustain that amount.
That being said, all the VISA engineers I've worked with are woefully incompetent, to the point they've spent 3+ months trying to integrate to our payment API, and we have to conference with them to help them out.
I'm talking one POST to our servers, and one browser redirect, most developers get it done in a few days.
Then when we integrated to them directly over individual banks (at their request, they paid a lot of money for this), their API was terrible, REST, RCP, XML, JSON, SOAP? Nope - a very strict space delimited text file, mean't to be read by a mainframe from the 60's.
We can't even send them ASCII text they use a different character set that competed with ASCII at the time of punch cards (sorry can't recall what it's called).
I'm sure they're mainframes are virtualized these days, but there system still acts like it's 50 years old.
In summary I'm sure they do some cool stuff somewhere in the company, but I haven't seen any of it. You'd be surprised just how much tape holds the banks and VI/MC together, they lose money all the time, have no clue where it goes, but as long as it's less then 10 million they don't really care, they just pay it out of their own pockets.