The 8030P in themselves perform very well. With the typical three-phases wiring in German houses, you will always find that certain rooms won't receive good signal if the pair of PLCs is on different power phases.

The ultimate solution to this is to add a Devolo DIN-rail 1200 PLC in the house's main fusebox, and run LAN from the internet router directly into that. This particular PLC will directly distribute onto all three phases straight out of the main fusebox. Keep your PA8030P and install where the client devices are - from my own experience with adapters from AVM, Devolo, Allnet and TP-Link, the TL-PA8030P have given me the most solid experience and best actual throughput.

Yet still, in my own house, I would have about 60 Mbit/s from the router to the office room up on the top floor. Other rooms were in the 60 to 150 range, using older AV500 gear. With the fusebox PLC installed, I now have 400 in the office, and 180 to 350 in the other rooms (still on AV500 hardware).

Also, to eliminate outside influence, you definitely need to establish an individually encrypted network. Pair your adapters using the button method.