[tgpc]

I would try two things:

(1) Running gigabit ethernet over the cat 5. Maybe it works?

(2) Look at GFast. I run a GFast service in my apartment block. We have Cat 3 (yes, 3!) cable. We can do 500mbit. You would need to buy a DSLAM.

[megasquid]

Thank you! I will look into that DSLAM.

[synicalx]

Fair warning, setting up and managing a DSLAM is an undertaking, and additionally everyone that wanted to use it would need a compatible modem as well.

Source: I've setup and managed two such environments back in the day at an ISP, and also a couple of older VDSL setups in apartment blocks. It's a good way of getting some extra mileage out of old wiring but its expensive, creates another SPOF, and requires at least some knowledge. It can also be a giant PITA to troubleshoot, and all your wiring becomes far more precious when it comes to water/damp and interference.