I had my room rewired with 4mm t&a and on a separate ring. I think the wire is Pirelli.
I don't know if it is better than 2.5mm but it does the job.
I did have most of the components plugged in to the wall on switchless MK sockets but there was a slight hum coming from the amps through the speakers I now have all plugged in to a Russ Andrews 8 socket board and then in to the wall. Dynamics are better and hum gone.
Thorens TD550, Ortofon 12", Ortofon Jubilee or Koetsu Black; Rothwell MCL SUT, VTL 2.5 pre, XTC POW 1 power; Naim CD5x; KEF Reference 3.2's; Van den Hul interconnects and speaker cables.