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.

We like Nvidia's decision to integrate a Gigabit Ethernet into its chipsets because this prevents motherboard makers from using lousy auxiliary GigE controllers that deliver poor throughput, high CPU utilization, or a little of both. That said, the GeForce's integrated Gigabit MAC doesn't deliver higher throughput or lower CPU utilization than a good GigE chip like Realtek's new 8111C.

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

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

We don't see much difference in PCI or PCI Express performance between the GeForce 8300 and 780G.