Ah fair enough. I thought it was DSL cables that were more prone to performance issues over anything more than tiny lengths. Well, compared to ethernet anyway
You can actually have a bit of length to the twisted pair RJ11 with no loss and the same noise protection
I can not have my modem right next to the master socket as their is no power in the hall so I pipe twisted pair RJ11 into the living room which is the closest room with power knowing there is little to no noise being sucked up like a cheap flat cable would.
Even if the modem was right next to the master I would still use twisted pair and don't get me started on ferrite cores haha
As long as it's good quality I guess that's what matters when using a longer cable. Luckily the guy who installed my socket placed it below a double power socket so I can afford to use a 0.5m twisted pair cable and then I run a 15m ethernet cable upstairs to my R1. The other power socket is reserved for a lamp lol.