Video card is only running at x8 instead of x16

[brokEN2]

Go into the BIOS and look for "Link Width" It defaults to auto so try manually setting it to 16x and see if that works.

I have pci port numbers 01 to 10 so which one would it be?

 

[brokEN2]

Also here are some other settings in bios that might need changing:

Gen2 High speed mode: auto and can be set to disabled, software initiated, advetised RC

Link ASPM: disabled and can be set to L0s, L1, L0s & L1

Link width: I set it to x16 instead of auto

Compliance mode: disabled and can be set to Gen2 or GEN1

 

[tigersty1e]

Reseat the gpu and then reset the cmos.

Sometimes the board needs to recycle the power for the connection to back to x16

 

[Grooveriding]

Try something.

Open GPUz and look at the bus speed, as you say, it is @ 8x. Open a 3D program in a window, maybe furmark or something would be the easiest.

Now look at GPUz and see if the speed has changed to 16x.

I don't know why but my motherboard does this for one slot, but once the card goes into use, the bus speed reads higher as it should. fwiw.

 

[Bearach]

Lots of good advice so far, you could also try inspecting the card. I had one card stop supporting above x8 because of a pair of these missing:

 

[KingFatty]

The difference between x8 and x16 is about 1%. So you would go from say 50 fps in x8 slot to 50.5 fps in x16 slot.

A website did a review using a 5870 and found that level of difference. So in actual gameplay, you are unlikely to notice any difference when switching between x8 and x16.

As someone else pointed out, using the lower x16 slot may cause limited airflow (your video card is really close to the power supply) and increased heat for the video card. So you may have a good reason to run the card in the upper slot at x8, because that lets the card run cooler at little/no impact to FPS.