Hi - first off, you are correct about the speed.
It is M500 whereas I must have read it could be an average of 550 Mbps.
Technically - that is the only point you have answered as you keep mentioning the MAC.
AND as I have said, I only used the MAC as a benchmark as it is next to the Hub3 - in the same room and that was purely for info.
I want to know why the dramatic fall off in the wifi speed compared to the range of the 350 Mbps we had previously towards the other end of the house.
As you also mentioned and I updated previously - I do not have range extenders either.