To achieve the optimum speeds, we recommend a wired connection to the router, using an ethernet cable.
There is no interference with a wired connection unlike a wireless connection.
A wireless signal is affected by distance and interference from other devices in the vicinity.
This is because each Wi-Fi device connects to a wireless channel and, when other devices use the same channel, it can influence the quality of your connections.
All of these are factors that can affect your speed.