PIC18F97J60 Ethernet performance
I have used the same chip from the same family (18F67J60) and I don't have quantitative data from its use, but your values are definitely significantly lower than I have seen (certainly my RX is many times faster than that).

One application I use with the chip is do bootloading via TFTP and I can receive information on the PIC at ~20k/sec or so.  I would look at how you're setting up your ethernet.  Perhaps the registers are set up incorrectly?  Is your ethernet hub bad?  I would try importing one of the basic examples from microchip (its on the C: in the microchip folder and has a few example applications) and see how fast its going.  Maybe use the Wireshark application to see the data going back and forth, maybe that will give you a clue as to whats happening.