Again, I'd go with a petrol 545i or even an RS6 with the 4.2TT lump in!
Both will come in well under budget (the latter by a couple of grand, the former by half) which leaves you plenty of cash to take care of any issues that crop up. Both will be a billion times more exciting than the diesel version, and even if you don't need the handling there's a lot to be said to have something with that much poke and with that gorgeous noise
Lowish miles aren't a requirement for these kinds of car, as they're premium so were designed to last. You're actually more likely to get issues with a diesel that barely breaks sweat than with a solid petrol car that's been used but looked after. Buy on condition, not on mileage. Servicing will be the same regardless of fuel type, just stick to specialists rather than main dealers.
It would be nice to have something special rather than just another dull barge, don'tcha think?