BT fibre optic modem because its fibre optic it needs to connect to the fibre optic in the master socket
Will the broadband speed by affected by moving it from the master socket to the bedroom socket? Yes because you will then be connecting by copper wire to the telephone socket.
Router is connected by cat5 cable to modem this is the start of the "slow down"
However all your other devices are limited by the speed of your home plugs or wireless connection.