As soon as you mentioned powerline adaptors and random varying speeds you tripped yourself up. Remove those and invest in a cat5/6 ethernet run.

Cyri

Edit powerline adaptor performance can change wildly and randomly with changes in 50Hz loading that is in no way related to computer networking. As such I view them as not fit for purposes as what may be good now is totally rubbish next due to a heater or stove element or heat pump turning on or off. As such in my view they are a waste of space