So, the EtherPort SE is a PDS card, and I'm using the AUI port with a 10base-T transceiver (MAU), which is hooked into a 10/100/1000 managed switch. 

The processor is stock - no accelerators present. Disk cache at 128KB.

I'm fairly certain the hardware is working fine, since I can sustain multi-megabyte transfers at ~60 KB/s using FTP. It's just AppleTalk (EtherTalk) that's terribly slow (10x slower).

Software is System 7.1, MacTCP 2.0.6, AppleShare Workstation 3.5, and NSI 1.5.1.