Since 5900x supports gen4 nvme I'd definitely be getting a gen4 SSD. Aside from being faster, there are additional technologies for gaming coming out in the form of RTX IO, Windows Direct Storage, and console equivalents.
My 2 cents
Don't think the end-user experience will be much different going from gen 3 to 4, this based on LTT blind test of SSHD / SSD / NVMe.
When NVMe 2.0 drops however I think we *might* percieve a difference.
I wonder if the requirements have changed?
MS states that you need a gen3 drive, Nvidia claims that you need a gen4 drive, someone has to be incorrect.
Microsoft DirectStorage is notably different to the concept put forward by Nvidia with its RTX I/O API, in that it copies the compressed data across to system memory before copying to the GPU VRAM. Once in the graphics card VRAM, the GPU can then decompress the data much quicker than the CPU can. Nvidia's solution works in largely the same way, although bypasses the system memory completely, and copies the data straight from the drive to the graphics card.
Agree for 10 bucks difference doesn’t make sense to go with a gen 3 drive now.