To achieve PCIe 4.0 x 4 you need an Intel gen 11 CPU. You system does not have the capability to run that SSD at maximum speed so the speeds you are seeing now would be the best you can get on your PCIe 3.0 x 4 M.2 slot. Keep in mind that x 4 is not the same as 4.0 x 4.
Hello, I have a 2 year old XPS 8930 motherboard with Intel i9-9900 CPU 3.10GHz. It was running very slow with the stock 1 TB WD HDD. I decided to upgrade to a Crucial P5 Plus 1TB drive. I used the Acronis Software from Crucial to clone my HDD. When I first connected the P5 Plus, I used a XPI X16 port to connect the M.2 SSD. I later realized that there was an M.2 right on the XPS 8930 motherboard. I moved the SSD to that port and am getting Read and write speeds ~ 3,500 Mb/S using CrystalDisk Mark 8. Not bad. The system is lightning fast compared to the SATA HDD with speeds of 197.9 Mb/s. However, the specs from the Crusial P5 Plus 1 TB SSD say I should be getting  6,000 Mb/s.  Crucial's rating is using a pci x4 slot for that rating. Are there any changes I can make to speed up that SSD? I noticed that the Dell setup has RAID for SATA. I am no longer using any SATA HDD. I tried changing it to AHCI, and my PC stopped booting. I then changed it back to RAID and system is working again, but am still getting below spec speeds of the Crucial SSD. Is there a maximum speed for the M.2 slot on the motherboard? I am NOT referring to the M.2 slot that the wireless card is plugged in to, but the M.2 slot in the lower right corner of the motherboard next to the 4 SATA ports. I am still using the same configuration that I had when I was using the HDD setup when system boots, but no HDD is connected. If I remove the HDD as an option would this be of any help?Thank you.
XPS 8930, questions regarding speed of an M.2 slot on motherboard