Had some practical experience with chip&PIN terminal debuginfo. For that particular hardware, transactions took something like 0.3 seconds to negotiate with the chip, 1.5-2 seconds to make the online part of transaction (most of it to establish a cellular data connection and the ssl handshake, the device had only 2G cell chip so very slow data :-/) but it all was dwarfed by the time needed to physically print the required receipt & confirmation; even we could make the transaction processing instant, it would be just a 25% improvement because of the printing speed.