Owned a 2005 LR3 and a 2012 LR4, I would say the LR3 is a better vehicle for dedicated overland rig, where the LR4 is sligtly better as a daily/overland rig.
The 4.4 was considerably more fuel efficient on and off road and is a more reliable motor in general than the 5.0, never really needed the extra power of the 5.0. Yeah the LR4 interior is nicer but the LR3 just has this perfect utilitarianess to it, my LR3 was only a 5 seater which gave it more space in the back, even after after removing the 3rd row seats from the LR4. I ran 275/65R18 on both and on the LR3 extremely minimal rubbing, where the LR4 had heaps of rubbing front and back, on the LR4 I would go a max of 265/65 if you don't wont to do lots of body work. Both of mine were HD packages and I would say they are about the same capability on really technical trails, the LR4 had slightly better traction control, quicker to engage the lockers.