the discovery 3 is an awesome motor for super cheap money, the 2.7 is a lovely engine but it is thirsty.
If you get a discovery 3 get a pre march 2006 and the tax is nearly half the cost, that what i had. unless commercial of course.
Discovery 4 3.0 lump is MUCH better on fuel like literately 10 pg better if not more, but same again get a post 2013? and its cheaper tax again anything inbetween is expensive. Plus of you get post 2013 you get the 8 speed box which with the 3.0 improves economy even more and is super smooth plus more power!!
My mechanic would have a 3 over a 4 just more reliable engine wise over here. Mine has 280000 on it at the minute and the newer oil pump not fitted to the pre 2008 which caused engine failure more often if not upgraded
The disco is back up trailer donkey really so if replaced with a 90 the 90 would just be a toy that can trailer when needed. 110 does most of it