I don't know how deep this rabbit hole you want to go down, but the speed of the transaction also depends on the actual chip in the card (ASIC), and the transce

I don't know how deep this rabbit hole you want to go down, but the speed of the transaction also depends on the actual chip in the card (ASIC), and the transceiver in the terminal. These chips do have to perform a cyptographic transaction while using power from the terminal. I wonder how much filth on the card causes poor connectivity(?). The max data rate for NFC is 848kbps (IIRC); not sure about contact smartcards, but it should be faster than that.