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 Asus' P5WD2 Premium motherboard with a Pentium 4 3.4GHz Extreme Edition (800MHz front-side bus, Hyper-Threading enabled) and PCI Express-attached Gigabit Ethernet. A crossover CAT6 cable was used to connect the server to each system.

The boards were tested with jumbo frames disabled.

You'll see that we've changed the names here and included a lot more results. All of our P35 and X38 Express-based motherboards use third party chips to handle Gigabit Ethernet, this despite the fact that the ICH9R has an integrated GigE MAC. The nForce 780i, however, integrates a pair of Gigabit controllers directly into the chipset, just like the 680i did before it. That leaves us with little choice but to compare networking performance on a motherboard rather than chipset level, so you'll find boards listed by name followed by their Ethernet source in brackets.

The 780i SLI's GigE performance shadows that of the 680i, and it's really not that impressive when compared with what third-party controllers offer. Only one of the 780i's GigE connections delivers full throughput, with the second stuck around 816Mbps. CPU utilization is higher for the nForce chipsets, too.

PCI Express performance
We used ntttcp to test PCI Express Ethernet throughput using a Marvell 88E8052-based PCI Express x1 Gigabit Ethernet card.

Apart from the P35's lower CPU utilization, there isn't much variance in PCI Express throughput with a standard Gigabit Ethernet card.

PCI performance
To test PCI performance, we used the same ntttcp test methods and a PCI VIA Velocity GigE NIC.

nForce PCI performance pulls up about 100Mbps short, though. And to make matters worse, it does so with higher CPU utilization—not a good combination.