But you have a 3L diesel, no? OP has a 1.5L.
I think i get where you're coming from though, he could get a BMW 530 diesel, but he isn't likely going to do that. We are talking about the 3L omega, and his current car...
10 grand a year is a lot of money to spend on fuel. It's so enormous that a more efficient car could literally pay for itself.
My point isn't that he should get the same car as me, more that doing 50k a year in a 20 year old 3 litre petrol Omega is a ridiculous prospect which makes absolutely no sense.
It's probably a less nice place to be than a Ford Focus these days.
Mileage rates generally drop after the first X thousand a year too.