Does anyone else use the PIC18F97J60 Ethernet capability? If so what kind of RX/TX performance is typical for that chip? I was running the TCPPerformanceRX/TX applications provided as part of the Microchip TCP/IP stack and getting between 1500-2000 bytes/sec TX and 60-80 bytes/sec RX. Receive seems way slower than it should be.
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.