I'm repeating myself a bit, but, dude, it's an 8088 (EDIT: ok, technically a NEC V20, pretty negligible though). It has an 8 bit wide bus. It runs at 4.77MHz and needs many cycles (at least 4? more?) per instruction. With a parallel port adapter, not even an 8 bit ISA one. I haven't done the math, not even on an envelope, but I somehow doubt the Ethernet adapter is the bottleneck here...