Originally Posted by Kremmen

I've kept track of about 100 transactions in 8 currencies on my Chase MC and Visa now. I'm mostly logging transactions that are posted on the same day on both cards, to keep them comparable no matter what the mid-rate is.

So far, the comparison to end of April vs xe.com is:
Chase MC: 1.0000 (exactly the mid-rate, to 4 significant digits)
Chase Visa (2014): 1.004124 (0.41% above)
Chase Visa (2015): 1.007236 (0.72% above)

This year, Visa transactions are so far over 0.7% more expensive than Mastercard transactions.