In the Bios I had made the following settings:
Settings > Advanced > PCI Subsystem Settings:
PEG0 set to Gen1
PCI Latency Timer set to 96 PCI Bus Clocks
Above G4... set to Enabled
Has anyone an idea why the performance is so bad?
Try to restore your motherboard BIOS settings to stock. And then set Gen2 on PCI Subsystem Settings, with PCI Latency Timer set to 32 PCI Bus Clocks. Use IGD for you Integrated Graphic Config instead of PEG. So connect you monitor directly to your motherboard. Try uninstalling your current nvidia driver with DDU and try to clean install newest driver or use driver version 384.xx. Hope it helps