I can't really compare the two, one is a Mercedes Vito 115 Cdi and the other a Jaguar X-Type 2.0 V6, they both average 26 mpg.
And I've not either long enough to have any meaningful service costs.
I think they only do this in a Quattro, if it's really that powerful I'd probably find the 2.5 TDi fine, I can't remember the last time I drove anywhere that allowed me to really open a car up anyway.
I owned a Range Rover for many years a 4.6 V8, it was horribly uneconomical I could get single figures on a bad day, but it's still the only car I've ever owned that I actually miss, everything else is really just transport.
Alan.