the best form of advice may not be what you want to hear. In the time you've been pontificating you could have bought a pair, tried them out and returned them if they didn't work. Our opinions, based on no knowledge of the layout, are worth about what you pay for them
It's often quicker and easier just to give it a try, put a router on one end of a homeplug set and go to the other and determine the packet loss over a few minutes.
Phil
666 kbytes/s with Demon
TalkTalk Dictionary : "Free" =