Most of Extreme's claim to fame through the years were their switches have always been "wirespeed" when it comes to packet forwarding. I can/t recall any time they have not met those standards and did not state the fact there was a limit of the amount of PPS the forwarding back-plane could handle. Since everyone pretty much uses the same chip sets and there are so many things we add to just raw ethernet frames that would affect your through put it is a bit hard I would imagine to list the pps. If i understand correctly the backplane and engine must support "theoretical " PPS by directional on all ports for all frame sizes for them to claim this.
I couldn't find it so far. Perhaps it's just missing in the datasheet or there is some limitation only Extreme is aware of.
For X590 it's also not specified as well BTW. 
