T i m wrote:
They may of course ... but what are the chances of an integrated NIC
(even an Intel one) being as capable (on a desktop board specifically)
as an add-on card, in the same way onboard video is rarely as capable
as even the simplest add-on video card (demonstrated by the size (lack
of?) of any heatsinks on the on-board video solutions)?

Gigabit is pretty mature technology here. It doesn't take much silicon
area, or much processing power these days: the link is likely to be the
limiting factor. I think it's approximately a cut and paste of the silicon
IP from the external NIC chip onto the motherboard chipset.
(Bearing in mind the ex-server 1G NICs you might buy on ebay are probably 10
years old, but still do the job)

If you're talking 10/40/100G then smarts in the NIC make a bigger
difference. You don't get those integrated (some mobos have 10G, but it's
an extra chip). That's also where thermals make more of a difference.

OOI, is there a utility that is good for doing such network throughput
tests or is it more 'real world' to transfer a largish block of data
(as I believe you mention previously) and just time the result?

I don't know of a tool, but in networking the relevant number is packets per
second, not Gbps. Most of the overhead is on dealing with packet headers
and so on, rather than shovelling data out the door. Lots of small packets
are more work than a few large ones.

Theo