I know you posted to disregard the thread but I'm also using a P5N SLI for virtualization (ESXi) and more than 3GB was nothing but a headache when using the onboard NIC. It would only function sporadically, it would look like its finally working then eventually it would just drop the connection and sit there picking its nose never to reconnect until a reboot. Disabled ethernet in BIOS, threw in a PCI-e gigabit NIC and haven't had any problems since.
Yeah Asus admits that there is a bug with the onboard NIC. And yeah it ended up dieing on me again so I threw in the old 100MB pci nic I had in it before.