Man, it took me a long time to understand your post !!!
So what you are doing is deploying what are called Home Plugs through your existing power cabling to transfer data from one room to another via Ethernet. Am I right?
If your house was wired in 1927, I am surprised you have any data movement at all. These power cables must be way past their prime (a able life is about 50 years) and would most probably have very high metal decay, very high resistance, and low shielding. The sockets would also be loaded with oxide coating and again create high interference. While using these for lighting and such, we usually don't bother and blame the EB for low light, flickering tubes, or a fan spinning slowly. or we employ a stabiliser to boost the power.
But if you are transporting data, it is a different matter altogether. Since the data transfer is not reliable, the two ends of the system will have to spend inordinate amount of time exchanging and verifying checksums to ensure the data packets have been received properly.
You have limited options and have to follow a planned methodology to isolate the problem. The issue could be with your cables, you sockets, a combination of the two, or just the specification of the installed cables.
1. Clean the sockets and, more important, the cables ends that are attached to the sockets. Get yourself some industrial grade electrical point cleaners to do this job. Isopropyl alcohol may not work. If you look at the end pints, they will be black in color with oxygen and iron coating when they should be copper brown. Another way to clean the end points is to scrape the end points with a sand paper or sharp knife and then clean it off with a cleaning liquid. Of course, if you have extra cable, just cut of the existing end points, and create new ones.
If after you do this you see some improvement in data transfer rates, you are on the right track.
2. Change the plugs as you mentioned.
3, Ultimately rewire the whole house.
One method I can suggest to see what is the issue is to create a external temporary circuit with new sockets and high gauge new wire. Just a meter or two will do. Just connect one end of the new wire to a power outlet (bare cleaned cable, not existing socket) to which you connect a new power socket. One the other end connect another new socket. Now use this temporary circuitry to transfer data and see what speeds you get. If you get good speeds, you now know what to do.
If possible, I would do this at the point where the EB connection is terminated (so called junction box) so that you completely avoid the internal wiring within your house.
Cheers
