Intel DX58SO stuck in PCIe 1.1 mode?

[HKPolice]

In the PCIe express configuration page, there is an option to disable/enable PCIe 1.1 compliance and it also shows the current link speed of each port. I've got a Radeon 4850 plugged in to the first PCIe 16x port and it's stuck in 2.5GT/s link mode which means PCIe 1.0 speeds

Enabling/disabling PCIe 1.1 compliance has no effect.

Using the latest 12/18 bios.

Any ideas?

TIA