Fastest SE-based Xbee? What is firmware 5122 for ?

I am trying to find the fastest possible mcu underlying Xbee for SE
because the app needs APS encryption. Using that, the throughput rate can drop significantly, and I need something like 40 messages per second at a router.

I noticed the effective rate is higher for the ZB SMT module than for the ZB Pro presumably because of the use of the Ember EM257. Unfortunately the ZB SMT does not support APS encryption. There seems to be a module (in X-CTU) that uses firmware 5122 for a XBP24CSE (Zigbee Smart Energy) and there is no further reference to it anywhere I can look. Does anybody know what that product is?

If Xbee is providing SE capabilites the underlying MCU’s should be faster. There are alternatives out there using 32-bit MCU’s, but I already have the API libraries for Xbee and rewriting is not an option.

I’m not sure about the MCU question, but the 5122 is the previous version of firmware for the XBee/XBee-PRO SE S2C module. The 5123 is the current/recommended Smart Energy firmware for the SMT module.