What do you consider bad performance? If you're using ISA cards you'll 
always be stuck to that limitation. If you're using pci or eisa or vlb 
cards you should be able to get faster throughput (at higher cost of 
course). I'm personally using a GVC NE2k ISA clone in my machine 
(486/66) and on a good day I get ~550k/sec over the LAN here. Outside 
our LAN I see much slower throughput so I doubt my card is the limiting 
factor there.  

Theoretically you're going to max out at around 1meg/sec at 10Mbps on 
any ISA card.
In reality you'll never see it though.

a 386/40 (pre-upgrade) with no load and 8megs of ram running 1.0 got about 
the same speeds with the same card.

cheers,

Brandon.