Why do you need another cable - j you already have one installed. Just use RJ11 patch leads from Master socket to the socket your Cat6 is connected to and then at the other end another from socket to Hub.
In a perfect environment 20m will make an almost imperceptible difference, however, in a home with lights, central heating, TVs, fridges &c there is a lot more noise to be picked up and the could impact slightly (or if you are unfortunate - significantly).
M H C
taurus excreta cerebrum vincit