PCIe 3 X4 -- no, an x4 drive won't run at full speed in this system.  
Does anyone know what version PCI an Inspiron 7570 has? I would like to put in a NVME Generation 4 drive, but I don't know if I would get any benefit. Does this laptop support PCI 4.0?   Thank you.
Inspiron 7570 PCI Version