My fuel "economy" is essentially terrible, well over 10l/100km in urban/commute situations, I'm lucky to get 320kms from a tank. Mine is tuned, so not a perfect baseline.
I eeked it down to 7.2l/100kms on a run to Pauanui and back some years back using a very light right foot and much cruise control, that wasn't much fun to drive though.
At the end of the day I only fill it up once a month or less (98) so economy is less of a concern to me than fun.
In "sport" mode, with both a flashed ECU and trans, I can see the fuel gauge moving down to empty when driving with spirit.
Not much point in owning a straight six lump if you're looking for economy I suppose.