It was ultimately an issue of duplex.  The netbsd nics were set to
autoselect, as was the switch.  Switch said "Full" and I have no idea what
the nics were other than how ifconfig reports autoselect.  I ultimately
hard-coded the whole collection of ports and nics to 100/Full.

It was interesting that the 3c905s/ex didn't bring up the FlowControl on the
switch as enabled while the i8255x/fxp's did.  So I'm back in my happy place
again.

I'm painfully aware of the issue with cisco cat's, but for some reason that
hadn't occurred to me here.

Thanks all,

peter