Advice on buying a new SUV

For the last ten years or so, I have purchased a new vehicle every three years. This seems to be the point where the balance between trade-in value and the price for a new vehicle is the best. (Am I correct in this assumption?) I am keen to buy another SUV, but the choices are increasingly bewildering. On my shortlist at the moment (in no particular order): Mercedes ML350 CDI, Audi Q7 3.0TDI, Porsche Cayenne TDI or S, VW Taureg 3.0TDI, new Jeep Grand Cherokee 3.0 CRD Overland (available later in the year) and BMW X5 3.0SD. (Not keen on the Discovery - really do not like the boxy shape). I do a fair amount of off-road driving, but not the really serious stuff. I do not want to spend much more than about R750k. Judging by some of the discussion on this forum, there are plenty of guys who are very knowledgeable about cars. Any advice would be greatly appreciated.