the i-plate purely disconnects the bell wire
No, it also filters out the noise picked up on your domestic wiring. You can indeed replicate the I Plate effect by cutting wires..... if you don't need any of your other sockets. Have a closer look and you will see some circuitry inside the device.
Remember that you will still need a microfilter at all sockets where there is a connection to a phone or device such as a Sky box.
BOAC, I don't think BT have many customers 5km from their nearest cabinet. FTTC is delivering a vastly improved service over the long line copper and BT recently announced that the up to 20Mb service will become up to 40Mb. Good luck with your new router but please allow 48hrs for the exchange equipment to notice and respond with a revised speed (hopefully better).