I'm really new to 10gbit ethernet... and learing every day
I read that cat6 should be ok until about 30m.
Connected my 2 cards with an existing 10m cat6 cable (goes through a wall).
But after some time the nics kept losing connection (media disconnected).
Tried drivers, power saving settings, bios.. all useless.
Before giving up I though I could try a cat7 cable... and voila connection perfect every time.