Thinking about buying a high mileage Allroad 2004/05 advice needed please!

Hi guys I'm new on here and am looking for a bit of general info.

I'm contemplating a fairly high mileage A6 Allroad with the 2.5tdi engine. I know these vehicles suffer from suspension problems so was wondering what to look out for when on a test drive.
In addition I'm thinking about the manual over the auto box though could be persuaded otherwise. What sort of realistic mileage could one expect from motorway cruising with the diesel?

Am I daft contemplating a vehicle that has 90k on the clock? I was pondering buying a Subaru but they are a tad agricultural and the Audi seems to offer a whole lot more for your money.

Cheers