Reduced performance of the video card on the Z800

[Sunktor]

Greetings
There is a question about the performance of the asus HD7970 video card.
At this station Z800 it shows a two or more times lower performance in tests compared to another computer.
I will certainly try to figure it out on my own, but maybe your tips will be useful.
Assumptions:
1) Perhaps the pci-ex slot works in 8x mode instead of 16 if you do not disable the second such slot by hardware from the BIOS, is it possible?
2) The motherboard bus is too slow, is it possible?
3) What other BIOS settings interfere with the full-price work of the video card?
Any ideas?

[Sunktor]

By tradition, I answer to myself.
The resource system diagnostic program showed that the PCIe port is in 8x mode. Attempts to fix this from BIOS have led nowhere. Most likely, to transfer the port to 16x mode, a special card is required, which is inserted into the second slot and converts it to the desired mode.
In addition, this motherboard operates only in PCIe 2.0 mode, which also limits the capabilities of the video card.
Changing the port settings has now just led to the inoperability of the video and resetting the smos does not give anything, just a gift motherboard ...