Powerchip and others claim 10-15% improvement in economy on the V8. So 10.9L/100KM would be maximum.
But looking at another way, a stock Td5 Manual can get 7.5L/100km. With rechip, de-egr and big intercooler driven for economy 6L/100KM is achievable.
Ultimately you need to have the car is perfect condition to do this. On mine the Transfer Case is getting a bit growly when cornering and at last oil change there was a bit of metal in the oil which suggests the CDL shims are cactus. I reckon things like that hit economy.
cheers
Paul

