I've had a fun day drilling holes in my walls and feeding cables. My ultimate objective is to have the router plugged into a filtered faceplate on the master socket, but as I mentioned elsewhere the layout of my house and the position of the master socket (in a window alcove at the bottom of the stairs) don't make this easy.
After some hard work I now have the router installed in the under-stairs cupboard, powered from a new mains socket I've fitted in there. A telephone cable comes from the master socket, under the stairs carpet, and through a hole in the wall to the router. A Cat5e cable with a wall-mounted socket at each end runs from the computer room, down through the kitchen, and into the understairs cupboard. A 4-port switch replaces the 4-port router to connect the PCs together.
I haven't yet bought the filtered faceplate, so I'm temporarily using a microfilter plugged into the master socket, but apart from that the job is done and it works. I'm feeling quite smug and self-satisfied.
When I've got the filtered faceplate I'll let you know if there is any significant improvement in performance.
Eric