Re:What is max PMP speed of PIC32?
Documentation shows how communication proceeds with zero wait states PMP and without address bus multiplexing and if I remember correctly it takes two or three pbclk's to transfer one block of data (8 bits or 16).
The other thing is actually doing something with read data. You'd need to at least store them in internal memory. Similar task is with writing to PMP: you'd need to at least read data to be sent from internal memory.
You may want to try to optimise in assembly routine that does this transfer and check what's maximum speed you can handle.