Johannes Stezenbach wrote:

What I'm interested in are some numbers for similar hardware,
to find out if my hardware and/or ethernet driver can be improved,
or if the CPU will always be the limiting factor.
I'd also be interested to know if hardware checksumming
support would improve throughput noticably in such a system,
or if it is only useful for 1Gbit and above.

Did anyone actually manage to get close to 100Mbit/sec
with similar CPU resources?

I have a pico station, http://ubnt.com/products/picostation.php with 
Atheros MIPS 4KC @ 180MHz.  Iperf on this device gives 46.0 Mbits/sec 
sending TCP from a PC to the device and 36.2 Mbits/sec sending TCP from 
the device to a PC.  The NIC is part of the Atheros chipset so PCI is 
not involved.
-ack