I've got a 51 plate A4 quattro sport with 3.0v6
They are certainly thirsty, I get about 23mpg average. I can get 35 out of it at 65 on an A road, but by the time you are up to 85 on a motorway, its back down to 25mpg. Probably similar to your 4motion. it gives 18mpg thrashing around town.
I had a 1.8T before this, and I love the 3.0! The biggest factor for me is the torque kicks in below 1500rpm, and it just pulls and pulls until the red line. There is absolutely no power band on this car, the linearity of response is fantastic.
You drive this for a while, you won't want to go back to small turbo engines.
You will also really appreciate the difference of the full time 4x4 vs the electronic clutch in the 4motion. The car balances superbly. The ESP can be a little intrusive, but you can always turn it off
Only problem I have had is coil packs, but go to a main dealer and they will change for free is under 100000miles. otherwise £25 each.
Currently having an issue with wheel bearings. Got them changed, but the rumble hasn't gone away. Back to the garage tomorrow.
It looks like a lot of fun for £5k. I have a pal with an old M3 who I joust with occasionally on the way to work. He can just about pull away in a straight, but the Audi wipes him out on a roundabout!