Hi Karl,
So many variables, we have got averages of 11-12's with no wind and straight flat roads at 90-100kms, and we have got 17-18's with wind and hills at 100-110km. Given ours is full height you should do a little better, as the other folk have indicated. No mods to our Prado just HR WDH and as Michael mentions tows really well.
Jas