This processor supports PCI Express 2.0, please check this link:
Is there an update available, so that this processor will be able to use PCIe 3.0?
What is the best solution when choosing a High-End Graphics card (as they are using 3.0)???
I have an XFX r9-390x-8df6, and would really hate to go backwards in order to find a card that is compatible.
This is related to the architecture developed for the processor, for that reason, an update is not available to support newer PCI-e 3.0 for these processors
What would happen if a PCIe 3.0 is used in a 2.0 slot is that your GPU will work at previous get speeds in terms of PCIe, that is mainly how it affects.