I wasn't able to get exact technical detail on the RAID behavior. However, the assumption is that the two 4X drives will run at the same performance as the 2X drive it's grouped with in the RAID 5. Same goes with RAID 0 and RAID 1.
As to your class 50 question: Drive classes and lanes are considered separate. Class 50 drives have slightly better performance than a class 40 drive. Class 40 and class 50 drives can work with either 2 lane support for 4 lane support. In other words a class 50 drive will have slightly better performance on a 2 lane port when compared with a class 40 on a 2 lane port. Same goes when you have 4 lanes and comparing performance between class 40 and 50.
Hope that makes sense.
I had the previous document I linked deleted. I now have a new document that is more clear regarding M.2 BIOS password support. Here: www.dell.com/.../no-bios-to-set-a-hard-drive-password-on-nvme-ssd
I will add it in to the original post.
I went back to Dell engineering and they confirmed that there are physical limits on the Vostro 5468 motherboard that only allow support for M.2 SATA. I've reported this fact to the documentation team and the NVME support claimed in the user's guide is going to be removed.
I will work on getting a better answer on the caching but it will take some time. I should be able to have the answer in a couple weeks, probably in the form of a brand new document outlining scope of support and the technical aspects all in one place.
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