My friend's grandpa & one of my uncle still own Pajero 5 door (1st gen). Don't know about Patrol but Pajero should give min 7.5kmpl city, 11+kmpl highways (may be 2kmpl offroad :p).
Both SUVs aren't suitable for local/regular use unless you've enough money
Never, Ever go for petrol engine, so you can put CNG & enjoy economy. If you do, your SUV would just become a "status symbol" but it'd lose power. Pakistani climate and road conditions are more favorable for diesel engine SUVs.
I doubt that. . . Diesel engines always give more millage than petrol ones. Talking about Pajero & Patrol, we take an example of a small car of that era. Daihatsu Charade (1983-88) 1.0 petrol engine millage varies between 13-17kmpl. But Charade Diesel (non-turbo) can go upto 22km in one liter. . .