Well, If you want detail;
The actual exchange rate for ATM and Credit Cards is based on the Interbank exchange rate based on the time that the transaction bank and your home bank (or credit card) complete the transaction. As mentioned, this rate fluctuates constantly during the day and is reported many places as either a spot closing (point picked in time) or a daily average depending on where you get your info or on criteria the banks agree on. At this level, you really get no better rate anywhere.
From there, it can get fuzzy real quick. Some banks may say that they charge no fees, but wrap costs into the above exchange. Others may delineate fees normally included, or may add fees. My Credit Union itemizes both an International Service Fee(ISF) and a Currency Conversion Fee (CCF), this sounds bad, but here is a real breakdown:
On Feb. 22, in Florence, I withdrew 200 Euro. If I go to Oanda.com I can see that the Interbank rate was a low of $1.3607, a high of $1.3642, and an average of $1.3619. That means, hitting an average, that 200 Euro should have cost me $272.38. Now my bank did charge me $2.16 for the ISF and $0.54 for the CCF, however, my total cost was $269.77+$2.16+$0.54= $272.47. Basically, my end cost was pennies different than the interbank average, meaning my credit union (or Visa that handles the debit card side) was able to get closer to the minimum rate, or there may have been some timing issue with previous or next day.
Many times I have done this calculation with the same result, my cost is 1%, usually less than Interbank, and usually difficult to tell due to normal fluctuation.
Based on what your bank is saying, you may be in the same situation as I, so use your ATM card. With a $600 limit (I get by on a $300 limit) you should be fine, any machine limit is overcome by making more than one transaction.