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.

There may only be one of them, but the nForce 780a SLI's integrated Gigabit Ethernet controller is pretty spiffy. Throughput is solid, and CPU utilization is very low. That's more than can be said for our 790FX board, whose Realtek GigE controller sucks up nearly three times the CPU cycles of the nForce 780a.

To be fair, it's up to motherboard makers to choose which GigE controller is paired with the 790FX. We've seen better Ethernet performance from other 790FX boards, but that kind of variance shouldn't affect the nForce 780a as long as motherboard makers correctly implement its embedded networking component.

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

Throughput is comparable here, but the 780a consumes slightly more CPU cycles than the 790FX.

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

Here the nForce has a slight throughput advantage and a bit of an edge in CPU utilization. Scores are very close, though.