We use a fairly basic homeplug for occasional use of an old PC upstairs in the opposite corner of the house.
We have a TT system with a split load box with each side having its own RCD. The upstairs power ring is on a different RCD from the downstairs ring. There has been some discussion here on whether this is a problem.
Unscientific and as reported by PowerPacket Utility:
Plugged in beside the upstairs PC speed is about 28Mbps
Plugged in to a socket the other side of the room about 32 to 40Mbps
Plugged into the light socket which is on the same RCD as the downstairs power ring about 48 to 65Mbps
It does therefore appear that the RCDs do make a difference unless anyone has any alternate suggestions.
All figures tend to reduce in the evenings. No extra electronics on but there are lights.