I replaced my OEM M.2 SSD with a 2TB Samsung 970 Evo Plus. Cloning was easy with Macrium Reflect. I also added two - 2TB Crucial MX500 2.5" SSDs in the U.2 drive brackets.

M.2 PCIe adapter is also an option.

Thanks, that's helpful! So, it seems that your Evo is taking advantage of the NVMe interface and hitting 3,500MB/s reads, while the Crucial maxes out at 560 MB/s.

I've had 27 years in the software business and I've yet to clone a drive lol. I may need to do so if that's the only way of getting the fastest read speeds from the M.2 SSD drive, esp. if they are 6x faster than SATA SSD drives.

*I was looking at these for comparison:

Crucial MX500 500GB 3D NAND SATA 2.5 Inch Internal SSD, up to 560MB/s - CT500MX500SSD1 : Amazon.ca: Electronics

Samsung 970 EVO Plus 2TB NVMe M.2 Internal SSD (MZ-V7S2T0B/AM) [Canada Version] : Amazon.ca: Electronics

Okay, so it sounds like if I want the same (or similar) read speeds* as my current SSD that's plugged into the only M.2 slot I have, I will need the M.2 PCIe adapter + Samsung 970 EVO. Then I'll get the 6000+MB/s read speeds (as per here). And this adapter will go in PCIe slot 6, and won't affect my upgrade options if I want to go with dual-GPUs at some point. Correct?

My only concerns are nuking a slot that may be the last slot of its kind that prevents me from upgrading to something I don't know I need yet (like maybe a Thunderbolt card).

*(I need max performance for video editing in Davinci Resolve. Since I started running out of drive space on my SSD and switched to caching clips to my SATA HDD, it is MUCH SLOWER.)

Thanks for helping me figure this out Prof!!

No, you cannot get anything higher than 3500 MB/S on your system unless you buy an adaptor that has RAID functionality and does not require bifurcation of the PCIE X8 or X16 slot to operate. If you are plugging that mentioned adaptor in a regular X4 slot that's going to provide 3500 MB/S at best.

I am pretty sure a regular SATA SSD is a much better option in your case, and you can always use 2 or more in a raid configuration if speed is a concern.

Try with 1 and see if the speed works for you. I am sure it will be fast enough.

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@EricJGML wrote:

My current config is 512GB M.2 PCIe NVMe SSD (Boot) + 2TB 7200RPM SATA.

Which is the best upgrade path?

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What I don't understand is how you ran out of room on your C-drive with 512gb SSD? That should be plenty of space for all Windows, Apps, Programs, and maybe even a couple of your favorite games. 

If you just want space for games, you can just install a 2tb SATA-3/600 SSD (and don't mess with C ). Remember, in Steam you can have multiple game folders. 

Personally, I would also replace that (big, hot, loud, heavy) 2tb spinner-HDD with a 2tb SATA-3/600 SSD. It will be much faster.

I didn't consider RAID, but I am now! With this adapter I can get two 2 TB M.2 SSD drives and use a RAID 0 config, get fast speeds and tons of storage. Thanks for the suggestion!!

Thanks for the warning, I'm just learning about "bifurcation" now. The specs only say:

I'm not an expert; but be careful with that linked adapter. I do not believe the Alienware motherboard supports bifurcation, and I do not see anything in that adapter marketing that indicates a controller for bifurcation to support dual M.2 drives.

This is an adapter that has a controller that provides bifurcation for a motherboard that does not support bifurcation LINK 

I'm a full-stack software engineer, so my boot drive has tons of development tools, SDKs, project files and npm packages, etc. Some data I can migrate to another drive, but that will take time. The main problem is there will likely never be enough room for cache clips from video editing software - which is currently taking up 150 GB on my HDD as I can't use my boot drive due to lack of space.

But since I'm now considering two M.2 SSD drives in a dual M.2 SSD RAID PCIe X4 host card with a RAID 0 config, I should be cooking with gas.