Servicing intervals on V6 TDI

Evening all, just completed my first service on the car, while I was resetting the service interval display on the dash, I got to thinking about variable servicing and all that mullarkey.( The handbook that came with the car indicates that it's on variable servicing.) Of course I used long life oil but I 'm wondering what the gurus Rotodiesel and Lummox think about how long you should leave it between services. Do you trust in the display to tell you when it's time to change the oil or would you recommend changes at a fixed mileage??? It gets driven pretty hard, and covers about 1200 miles per week, mostly through flooded roads because I live in Ireland.!!!:D:D Let me know what ye think......