XPS 8920, SATA ports, are all 6 Gbps?

The specifications only lists 6 Gbps which is SATA III. There are no SATA II interfaces, but SATA III specifications provide backwards compatibility to function on SATA I and SATA II ports.

I plugged my 2.5 ssd data cable into one of them but don't know which one so I guess it doesn't matter. Right?

I don't think it matters which SATA port although some have said the boot drive should be connected to the first SATA port (SATA1).

"The general opinion is that only # 0 and # 1 mobo connectors supply sata 3 (6gbs)"

Not sure where that opinion originated?

The online XPS 8920 Setup and Specifications PDF only mentions SATA as 6 Gbps. It never mentions SATA as 3 Gbps.

The online XPS 8920 Service Manual shows the following on page 17 =
Port 4 = SATA 6 Gbps for hard drive (SATA1)
Port 5 = SATA 6 Gbps for optical drive (SATA2)
Port 6 = SATA 6 Gbps drive connector (SATA3)
Port 7 = SATA 6 Gbps drive connector (SATA4)

So why would anyone think that two of the SATA ports are NOT 6 Gbps?

I don't know but I have read in many places that only 2 ports are rated sata III and the others are sata II.

Good info. I guess I am back in my 8500 days because that was my last computer too (It served me very well). I plugged my 2.5 sata Samsung ssd into a random port on the mobo of the 8920 so I guess I can leave it there. I bought a Samsung 970 NVME M.2 and tried for 3 days to get it to work, sent it back, and got the 2.5. I was waiting for the little hold-down screw to arrive so I had it plugged in at the 30* angle which some say doesn't matter and some say it does. I hope that wasn't my only problem. 

The chipset isn't quite right for installing Windows on an NVMe SSD.  The chipset in the 8930 is.  However, you can do it.  Avoid the Samsung NVMe drives.  The one that works for me is the one shipped with my 8920.  It is a Toshiba KXG50NVS 512GB.  The problem is that the seventh gen chipsets require a driver before the chipset can see the drive.  I used the Intel IRST drivers saved to a usb.  The trick is to disconnect all other drives except the optical drive, install the NVMe drive, boot with a Windows 10 dvd and start the installation.  When volume picker page appears,  select load driver and point the installer to the usb.  After the drivers load you will be able to see the NVMe drive so you can select it and proceed with installation.  It is worth doing.  My Toshiba drive hits 3000 seq read.  My 2.5" SSDs only do 550.  Write speeds are comparably faster also.

It seems to me that Dell would fix the install of NVME's so you don't have to jump through so many hoops by now but since I gave up trying to install the MVME and opted for a 2.5" sata drive I will wait another 3 1/2 years to try it again since I buy a new Dell every 4 years.

Why is it so Difficult to get the CORRECT ANSWER to set up a RAID 0 on an XPS 8920 ? what is the correct path to set it up ? I have 2 M.2 Samsung 960 pros i have been trying to set up and it wont go..... I have no problem setting one up with windows 10 but cant get it to RAID 0........Please provide the proper ANSWER.