I have an evga classified sr 2 motherboard. Take care of this mb because ifvyou have two xeons installed and need a quad cg config, you will need two have at least a 1500w power supply! If not, you will not able to run four graphics cards but  just three of them 

Unfortunetly, I have only a 1200w power suplly and it is not sufficent to power two xeons 5650 and four evga  580 3gb. So I have to deinstall one Gcard... If I want to keep the four gc, I would have to remove a xeon!
Work Station : MB ASUS X299-Pro/SE - Intel i9 7980XE (2,6ghz 18 cores / 36 threads) - Ram 64GB - RTX4090 + RTX3090 - Win10
Net render : MB Asus Pro WS W790E-SAGE SE - XEON - 128GB - 2 x RTX 3090 - 3 x RTX 2080TI