Personally I would go for a petrol model. No, not all models come with the diff-lock. You do get a 24V DOHC 3L (130kw), it is a bit of a pain to work on (you have to remove the intake to change plugs etc unless you have a special tool, same on the 3.5 models) and scarce. Most of the 3L are the 12V SOHC model (104kw), which are great engines. You get the 3.5 GDI DOHC but it is not much loved (even though it has around 170 odd kw) due to high maintenance costs. You do as mentioned get the 3.5 SOHC, but most are the 3.5DOHC(150kw).My first choice would be (and was) a 3L SOHC, followed by a 3.5 SOHC and then the 3.5 DOHC (non-GDI)
then you get the Pajero Evo which has the 3.5 MIVEC DOHC which gives you about 195kw, yes, I WANT ONE!