before I go of in a useless rant about what I use to get, What's a ground wire kit?
edit: scratch the ground wire - found it! (this must be my month of the 'tard attacks!)
I haven't actually done the experiment yet (pinny's off the road - dam money!)
back when I was driving it full time I use to get about 550 K/tank (approx 50 L) on standard unleaded (back when it was about 79 c/L long time I know!) it was about 90-95% open road, the rest was city driving, I had to do about 3 K of dirt track first and last thing (the joys of living on a farm). about 50 K/tank was a direct gain from the cruse control. I use to run my Tires at around 30 psi.
The main thing I remember was I could get about 300-350 k on half a tank, then it use to drink the last bit.
of course these figures are based on me behaving the entire time, the worst I ever got was a touch over 380 on just under 50 L.
once I get the old girl back on the road (new drivers seat, fix panel damage, service, I think she needs new rings sometime soon, oh and I'd better fix that oil leak!)
PS if anyone thinks this rant isn't at all relevant let me know and I'll delete it back to the original question.