Langman if I may ask why do you want to change?
I don't know whether you drive your Patrol daily, or only play with it, but let me share a sum with you:
I am currently planning a trip to Bots for early next year. The basic trip is JHB, Martin's Drift, Kubu, Maun, Moremi, Savuti, Linyanti, Kasane, Palapye and back to JHB. Total trip distance is 3125km (this does not include game drives, but they are normally inconsequential). Total trip cost is estimated at R21 295.07 for my family of four in my 4.2 Patrol (which is heavier on fuel than my friend Tinus's 4.8). My estimated trip cost in a 3l Patrol would have been R19 133.68, so a saving of only R2 161.39
This does not include the maintenance or depreciation on the vehicle, but I beleive the long-term maintenance on the Diesel is more than on the Petrol.
I think that if you change, you will lose on the deal unless you are very lucky, but if it was me and I had to change, I would be going for a 4.8.

Mag ons ons kenniskry met lekkerkry aanhoukry.