2008 Audi S6 to buy or not to buy?
 

Currently I was in the market for a new car, I think its about that time. I'm currently driving an 06 Mercedes R350, and its a great car.... for families. Its huge, and all over the place and already has had a transmission failiure which I'm so glad was covered under warranty. I've a;ready added a ton of clicks on it so I began looking at audis until I came across the Audi S6, the one that comes with a V10 engine, the 2007-2008 model.

I dont mind the gas mileage at all, I know it's gonna be bad. I think this will be the same on gas more or less $20. All im wondering is what kind of problems should I expect with one that has 90k Miles on it? I found one listed for 16k but it looks super clean, and no accidents, well reviewed dealership.

I also found one with 70K Miles with the same things as above but its listed for 21k.

So I'm not sure if i should dish out the extra $5000 for 20k less miles or not.
I dont drive much maybe, 7k miles a year, mostly city driving. I did the same thing my current vehicle. Also if anyone lives in ontario, toronto, how much is it to ensure one of these things?