I dropped the A3 off today at Macc Audi for its new steering column replacement due to a creaking noise and they have given me an A4 Avant 170 Diesel.
First thing i noticed was that its alot smoother than the 140 Diesel (we have A4 Avant 140's as Poole cars at work).
Power wise i didn't really notice a massive difference from the 140, I didn't actually know it was a 170 until i got a call from them updating on my car which was when i asked them about it.
It is certainly faster top end and much much smoother than the 140, and i gotta admit i do enjoy it, if i was doing high mileage then i would get one but its still petrol for me.
No way as fast as the 2.0T but then again the A4 is heavier than the A3.
Thumbs up from me though and thats saying something as i hate diesels!