For future proofing it can be worthwhile to get a pcie4 drive for a pcie3 machine.
That said, even if you have a pcie4 machine it may not be worth it to bother with pcie4 storage. I was annoyed about loading times with baldurs gate 3 and decided to try installing it to a RAM disk (yes, using 130GB of RAM)… Barely loaded any faster. Turns out the main bottleneck is elsewhere and my storage was not the issue
New world