I usually use bp ultimate and got about 400km per tank
But i changed to a k&n filter, 3in turbo back and upped the boost to about 10 psi.(about two weeks ago)
I am now getting about 460-500 per tank (red light for the last 30km)
Everything stock except the above, still using bp ultimate..
I have found in the past that caltex/woolies petrol never gave me as much k's
96 rs4, btw