My dad has a huge mileage headstart on me - he is up to 12k miles in his GTD, had his first service at 9.5k miles and hasn't seen any appreciable gains in mpg or performance, it is as it was when new on 1st July. Anyone expecting the GTD to be significantly better on the MPG than it's predecessor is probably going to be disappointed. Expect 45-47mpg on short journeys (less than 15 miles) in the winter, 50-52mpg in the summer, and maybe pushing 58mpg on a long trip in the summer without driving like a nun.