First of all i am throwing out data which i have read on Pakwheels posted by experts here.
I dont remember if there is some 2.5 liter diesel in second gen pajero.
Even if it is present then it is prone to heating up on motorway.
2.8 intercooler turbo is the minimum.
If you look at the 1st gen then 2.5 diesel is the most common.
Old diesel's dont give more then 6 or 7km/liter. That is again best figure under ideal conditions. Worse is you can get 4km/liter.
Go through the 4x4 section you will find many threads which you will find use full for buying decision.
Sportage is mostly running on toyota engines these days.
Costs from 4 to 6.5 lacks depending on condition. But it does not have spirit of a true suv as per me.