Hi,
speed is not directly determined by the used RF frontend but rather by the overall system partitioning. If you compare both devices, RC522 and PN532 there is one big difference: RC522 is a hard-wired logic, register based frontend. All hardware and protocol abstraction logic has to be implemented on your microcontroller.
PN532, on the other hand, is an integrated NFC controller so hardware and protocol abstraction runs diectly inside PN532 and is tightly coupled with the contactless interface. On host micrcontroller side only a few commands have to be sent in order to activate/detect a tag for instance whilst RC522 requires multiple low level register operations, each operation results in a single SPI/I2C transfer. PN532 performs this low level register operations directly onchip (inside PN532), so one register operations takes not even 1us. Writing a register from a host microcontroller into RC522 can take several hundred microseconds (counting software overhead, SPI/I2C transfer times etc.)
So looking at these facts I would say from overall system perspective PN532 could operate much faster than RC522.
Advantage of RC522 of course is a higher flexibility, since host micrcontroller has direct register access to the contatless interface hardware.
HTH,
Christian.
