That's the road to ruin for WiFi. Don't do that. I'm not going to repeat prior discussions on why and more. There is something to know about powerline which is covered by the maker. So I'll keep it short. The powerline devices have to be on the same side or phase of the mains circuit.
As to true speed, no one can tell you as each mains wiring varies a little. It's not as bad as WiFi can varies since no one else shares the air space (WiFi) but on the mains, it's just these 2 things.
Hi, I have the BT Master socket and Sky Router in a small office at the rear of my house. I get download speeds of up to 40Mbps via Sky Fibre Unlimited Pro (Fibre to cabinet not the house). I want to move my office upstairs to the front of the house. Wifi reception hasn't been brilliant so I bought a Sky Wifi Extender which is rubbish. To compound matters, I have a PC in the upstairs room running 3 CCTV cameras (via an ethernet switch), hard-wired into my Sky Router downstairs. The CCTV software records 1080p video on movement detection onto the PC's hard disk.
So, here's my question. I'm moving my office upstairs and putting the CCTV server in the attic out of the way. However, I don't think it'll get a signal from the Sky Router at the back of the house, especially with the bandwith needed for the cameras. I'd thought about having the BT Master Socket moved upstairs but my wife hates cables/trunking, and I fear Openreach will have cables running from the entry point under my porch, all over the place to get upstairs. I'd thought about a super-router and then someone suggested Powerline 1200, which I know isn't a true speed and can be degraded by all kinds of things with the electrical signal.
I need coverage upstairs, in the attic, downstairs (SkyHD+), and the conservatory. I'm approximately 3500 sq feet of living space.
Any experts got any suggestions? Thanks very much.