Driving like an old lady

[306pc]

Just wondering what's the best fuel consumption everyone has had from our various states of tune?
I've just eaked 592 miles on a tank with a 9mm Bosch lda grind and gov mod and a GT15 making 20psi. I was very impressed with this return even if it did mean I had to drive like mother Theresa. Apart from the 2 times I had goons following too close so I booted it to cover them in black smoke! They soon back off. :-)
If I boot it everywhere I can get as low as 400 miles per tank, so it does make quite a considerable difference. Anyone beat 592?