Alpina D3 S vs BMW M340d - Just an M340d Turned up to 11?

Hi, and join me on a very interesting road test between two very similar cars. But how similar are they? Too similar for the Alpina to be worth its hefty asking price, over the base car from where it began? Join me on this twin test, where I try to explain the difference between a great car and a special car! It wasn't easy! Hope you enjoy. Stephen