I would say performance is so contingent on wiring quality that it cannot be reasonably assured. I tried out a TPLink system that claimed to be able to deliver 300 mb/sec and only managed 10. The fundamental problem is that you tend to want to place the units in areas with the highest potential for noise (eg near lots of electronics).
Your experience is typical even in the cleanest of AC power conditions. Powerline is hilariously oversold and regularly provides less than 25% of the advertised throughput.
The "2 gigabit" adapters top out at 470mbit when both sides are plugged into the same duplex receptacle. That number is cut in half when you move to another room, and it gets worse from there.
Every Powerline vendor, without exception, are using funny math when coming up with their advertised throughput numbers. In no situation will they ever be able to provide 50% of their stated throughput, and more typically it's closer to 10%.
