I've tried the drivers from the CD, Gigabyte's site and Realtek themselves and none seem to work. I just did a reinstall and used the ones on Gigabyte's site (7.48.823.2011) so we'll see what happens.
Edit: Windows Network Diagnostics Publisher details
Issues found
The Realtek PCIe GBE Family Controller adapter is experiencing driver- or hardware-related problemsThe Realtek PCIe GBE Family Controller adapter is experiencing driver- or hardware-related problems Detected
The wired network adapter is experiencing problems Completed
Issues found Detection details
6 The Realtek PCIe GBE Family Controller adapter is experiencing driver- or hardware-related problems Detected
Detection details
Diagnostics Information (Network Adapter)
Details about network adapter diagnosis:
Network adapter Local Area Connection driver information:
Description . . . . . . . . . . : Realtek PCIe GBE Family Controller
Manufacturer . . . . . . . . . : Realtek
Provider . . . . . . . . . . . : Realtek
Version . . . . . . . . . . . : 7.48.823.2011
Inf File Name . . . . . . . . . : C:\Windows\INF\oem8.inf
Inf File Date . . . . . . . . . : 17 October 2011 09:21:52
Section Name . . . . . . . . . : RTL8168E.ndi
Hardware ID . . . . . . . . . . : pci\ven_10ec&dev_8168&rev_06
Instance Status Flags . . . . . : 0x1802400
Device Manager Status Code . . : 10
IfType . . . . . . . . . . . . : 6
Physical Media Type . . . . . . : 14
Network Diagnostics Log
File Name: E824EA3E-8CFB-4357-B4C4-5D460B802ECC.Diagnose.0.etl
Other Networking Configuration and Logs
File Name: NetworkConfiguration.cab
Collection information
Computer Name:
Windows Version: 6.1
Architecture: amd64
Time: Thursday, March 15, 2012 7:53:53 PM
Publisher details
Windows Network Diagnostics
Detects problems with network connectivity.
Package Version: 1.0
Publisher: Microsoft Windows
Edit: I managed to fix it (at 2am) by switching everything off, unplugging the PSU and draining the capacitors. I'm guessing a Rom somewhere got confused and had troubles, but it seems to work fine. Even manages BF3 on mostly high settings at 1920x1200 with framerates averaging 34/35 on an HD4870.