Just to add to the thread...
Just had 32" BFG A/t's fitted last Wednesday (before I had the factory size 29's on the stock DX rims).
Before the new tyres would always get 10km/litre (according to the cars odo).
Just got home yesterday after a run to Melb and back (2000 round trip).
Now down to 9.1km/litre (according to odometer) but actually 9.6 according to GPS (sitting on 110 the whole way down and back).
Interestingly the speedo is now spot on, but odo is out by about 6%, which I was expecting given the difference in tyre diameter.
I'm still running the factory exhaust and haven't done anything with the EGR but that will change in the next month, so I'm looking forward to an improvement there.