I drive a NCII Sportsman, which comes with the ED XR6 engine and some other bits and pieces. I also had a 5.0 litre NCII until recently but fuel costs were pretty high for a car that didn't go any harder than my Sportsman. My 4.0 ltr Sportsman averages 11.4 or so kms per 100 K's of mixed driving in and around Canberra. Thats worked out over 6 or 8 tanks. My V8 averaged about 15.5 doing the same driving.
My car has HM headers, 2.5 inch Cat and Exhaust, K&N Filter and a Unichip and uses less fuel with all this fitted, goes harder than the V8 now as well - Just doesn't sound as good!!!!