> TCP buffers too small, and other values not tuned, see [1]?

It could also be differences in parameter settings for interrupt
coalescing.

> Though IIRC there was something about auto-tuning those buffers, but
> I don't know if that's enabled by default (or how to enable it if
> not).

On a sufficiently new kernel, you could put this in /etc/sysctl.conf

net.inet.tcp.sendbuf_auto=3D1
net.inet.tcp.recvbuf_auto=3D1

to enable TCP window auto-tuning.  This functionality arrived in
NetBSD-current on August 7 this year, and will not be in 4.0.

Regards,

- H=E5vard