For gaming the speed difference honestly won't matter.

NVMe drives are really only faster for sequential workloads. For random IO like games, your OS, opening programs, etc. a decent SATA drive and an NVMe drive barely have a performance difference. Then even that what little performance difference there is would be erased, and then some, due to the USB overhead of using the NVMe drive externally.

In this situation, I would honestly just go with what you can get cheaper.