I have fiber coming into my flat and connecting to an Eltex NTE-RG-1421G-WAC modem/router combo via the PON port. I wanted to get an Asus RT-AC88U router but I am concerned about speed loss. The Eltex NTE-RG-1421G-WAC modem/router combo does not have external antennae. I am not getting a strong signal in the back of the flat and even next to the router on my iPhone, I get about 90 Mbps download and 75 Mbps upload on the Speedtest app on the 5 GHz band. The ISP advertises 100+ Mbps speed. I am going to contact the ISP about the less than advertised speed but my primary question remains, will I see speed loss by adding the Asus RT-AC88U router? If so is there a better solution?