This might be a little off topic but... it seems like this list has
the most knowledgable people concerning Mac hardware.

On old Macs, (centris) I seem to remember that the serial port speed
should not be set above 38400 because it just can't keep up.

I recently picked up a 56k modem (SupraExpress for $30!). Anyway, it seems
that leaving the port speed at 38.4 won't take advantage of the speed.
Since NetBSD streamlines the OS from what MacOS, is there any chance of
speeding up the port speed or am I stuck?

Using the modem at 38.4 kinda defeats the purpose, and using it at 56k
on my MacOS PPC leaves my network (and MacBSD) cut off from the world.