3.9i or 3.5i ???

Hello guys, Im still looking for a disco, Im after a manual v8i on gas, i have my eye on two, a 3.9 with a good spec or an old 3.5 thats kitted out for off roading. I dont want an auto, I just dont like them and i dont fancy swapping a box over any time soon. So what im asking is... What are the main differences between the 3.9i and 3.5i power.. gas mileage.. reliability etc.. Do all these engines suffer with the head problems like my friends 4.6hse p38? I've done some searching but came up with nothing, Thanks guys. Nick.

4.0

soon as they started dickin about with the 3.5 to increase the capacity it all started going downhill.
for me it has to be the 3.5