I can only confirm your problems, my Compaq-P75 with onboard PCnet-PCI
   has reported
    Mar  7 00:05:23 dirty /netbsd: le0: framing error
    Mar  7 00:05:23 dirty /netbsd: le0: crc mismatch

You're talking about two *completely* different things.

One is a DMA underrun, probably due to some other device hogging the
bus.  The other is most likely a transmission error from another machine
on your network.