3.9, if only because of the complete TCP/IP stack that doesn't time out after 30 minutes, or need a couple of hours configuring like amitcp...
anything with a 3.1 rom, an 020/030, a couple of meg fast should be able to run 3.9...
if i can run windows 3.1 under PC task on a 25Mhz EC030, 3.9 should be fine
