LR Disco2 is v8 4.0 petrol. In town, if you get 15mpg you are happy man. This summer I drove it from here to Serbia fully laden, it was averaging 18-19mpg. Through Germany, I did not drop below 140km/h... I found GL420 not much worse in fuel efficiency from our old 2.2 Renault Grand Espace, which is impressive for almost twice the size and power engine.
Still need to go and get a few bags of sand and put them in the boot and see if that improves handling and over-steer on ice/snow...