Here is another data point. It appears that at least some ATMs are matching the credit card rate for cash withdrawals. I used a visa branded ATM card and withdrew 15,000 ARS. The initial rate was ARS287.69 / USD. However, there was a bank fee bundled in there. My bank will credit that fee at the end of the month and I expect the final rate to be something like ARS319 / USD.

I won't be testing this further as I am only using cash for tip money but others might want to experiment.