This probably belongs in the mpg thread, but as it's achieved with the DTUK box on, I thought I would comment here.
Took a trip down to Leeds today (105 miles each way), by far the furthest my GTD has been since new.
On the way down, 22C ambient temp in the morning, stopping at Stockton 1/3 of the way down and doing 80mph all the way down the A19 and A1, the car averaged 55mpg (indicated). The car was in Sport mode and the aircon was on all the way.
On the way back, it was 27C ambient until we were around Durham and it clouded over, dropping to 22C. The car was looking to be managing 57mpg doing 80mph all the way back until we hit about 6 miles of 50mph roadworks with average speed cameras and the mpg climbed steadily, end result for the return journey was 61.4mpg, doing 80-85mph (apart from the average speed camera zone and a few spurts to 90mph).
Bear in mind that the car is reading 9% optimistic with the box on vs 3% without, we're probably talking about equivalent indicated stock 52mpg/50mpg actual there and 58mpg stock indicated/55mpg actual back - with the aircon on! A smidge better than the best ever with my Scirocco (59mpg indicated/54mpg actual) on a 350 mile journey.
