Cat 8 is real.

“Category 8 was ratified by the TR43 working group under ANSI/TIA 568-C.2-1. It is defined up to 2000 MHz and only for distances up to 30 m or 36 m, depending on the patch cords used.”

https://en.m.wikipedia.org/wiki/ISO/IEC_11801

That cat 5 cable is probably fine… you don’t need cat7 or 8. At most cat 6 or 6a, but honestly cat 5 can do gigabit.

No it isn’t pointless and yes it will make a difference. An Ethernet cable isn’t going for half its bandwidth when a microwave turns on.