After more than 15 years driving BJ60s, mileage has been as high as 34MPG at 90kph with super skinny Michelin tires (can't find them anymore, I think they were 7.00/100R15) on summer diesel, but usually on my Canadian Tire Roughriders (235/75R15) they averaged about 30-32 at that speed and driving conditions (summer going to Maine constant 90kph). This is 9l/100 territory here, folks!
In winter, I've gone as high as 22MPG, usually around 24MPG which is about 12-13l/100. This also corresponds to average 30km drives from a cold start.
Compare that to the HDJ81, with 4.3L turbo diesel, which I have been able to run as low as 10.2 l/100 (about 28MPG) on _winter_ Nokian Studded Tires, but which usually, for the same type of distances (30 km runs from cold starts), will use between 12 and 14 l/100 (about 10% more). Notice I stopped using the old 'MPG' calculation anymore...
My figures are compensated for tire size as measured from highway km marker distance. Driving style with the HDJ81 is markedly more spririted, of course...
There you go. Hope this helps a bit... Factors to consider, besides driving style and distances, is tire size, profile and type. Wider titres definitely use more fuel. Been there, done that. When I got my first (running) FJ40, it had those huge super wide super swamper type monster tires on it, and it was unbelievably thristy (10MPG) until I replaced the wheels and tires with something more reasonable (16MPG).