a thousand curses on the people who built this house and then wired it with cat5
Not even Cat 5e?
That's just... twisted (pair).
Tangent: how is Cat 6 over 2 decades old now???!!!
Should still be enough for 5Gbit and if you're lucky even 10Gbit from what I've been told. Still can't quite believe that things improved that drastically from when I started into the industry though...
(2.5G I can confirm, that worked over a few meters of shitty cat5 a few weeks ago when I tested it)
Edit: Wikipedia says 2.5G is the max for Cat5.
CAT6 can do 10GBASE-T over 55m
CAT6a over 100m
Some on reddit said Cat5 can do 10Gbit depending on factory tolerances as well.