The Desmond is pretty reasonable with a proper gearbox, and it's quite rev happy.
Never owned a 2.5/3.0 but found the 3.2 manual to be pretty decent on fuel using the same criteria as above
2.2 needs to be a manual*, and you need to rag the nads off it all the time. It'll never win any races, but can be a laugh.
The 3.0 is in a different league, economy wise, to the 3.2, when driven the same. And I'd argue slightly better on acceleration as well (with the same gearbox), though not by much. Still wouldn't use one for a taxi, though!
*The only single exception I've ever driven was Auto Addicts old 2.2 auto, that thing was the best, quickest 2.2 auto I've ever driven. It went like the clappers, and was clearly driven at
90mph 45mph everywhere.