Ethernet performance
We evaluated Ethernet performance using the NTttcp tool from Microsoft's Windows DDK. The docs say this program "provides the customer with a multi-threaded, asynchronous performance benchmark for measuring achievable data transfer rate."

We used the following command line options on the server machine:

ntttcps -m 4,0,192.168.1.25 -a

..and the same basic thing on each of our test systems acting as clients:

ntttcpr -m 4,0,192.168.1.25 -a

Our server was a Windows XP Pro system based on Chaintech's Zenith 9CJS motherboard with a Pentium 4 2.4GHz (800MHz front-side bus, Hyper-Threading enabled) and CSA-attached Gigabit Ethernet. A crossover CAT6 cable was used to connect the server to each system.

The nForce4 boards were tested with the NVIDIA Firewall and Jumbo Frames disabled.

The K8N-DL's PCI Express Gigabit Ethernet chip offers higher throughput and lower CPU utilization than the nForce Pro's ActiveArmor-accelerated GigE. ActiveArmor isn't working right with NVIDIA's current ForceWare drivers for K8 platforms, and NVIDIA is aware of the issue. We've seen beta drivers drop CPU utilization with ActiveArmor to between 10 and 12%, but those drivers have yet to be made public.