You've got to look at the running costs when running as a Taxi, aren't the Jag parts and service costs really expensive? I guess you are aiming at a more exclusive clientele?
The 3 litre is a lovely engine though and IMO much better, stronger and more refined than the 2.7.
Have you thought of a used Phaeton? They are fantastic value and come with some really nice engines and plenty of luxury toys and servicing costs are on a par with a Passat.