Because the service is delivered over a fibre-optic cable from the exchange to the new fibre cabinet close to your property, this service will offer a much higher speed than any ADSL or ADSL2+ service (including LLU) currently on the market.
Most properties are going to be within 500 metres of their cabinet, so there is only a very short run of copper wire rather than several miles. Add this to the new VDSL2 signal and it provides speeds of up to 40 Mb downstream and 10 Mb upstream.
BT Openreach say they will guarantee a minimum of 15 Mb SYNC speed on the Fibre Broadband service, therefore there will almost certainly be a speed boost for most current Broadband users.
A property that is less than 300 metres from a fibre cabinet is likely to achieve 30-40 Mb downstream and 8-10 Mb upstream.
Another major improvement will be the stability of the line. Because the majority of the line is on fibre-optic cable there is not as much copper degradation, and thus a higher quality line all round.