I put some Shell V-max (the more expensive stuff) in my Morris 1000 the other day after reading about it in the owners club magazine. I had to slightly retard the ignition and BOY what a difference. Pulls so much better, I was really surprised and will be interested to see what the MPG is. So much nicer to drive- smoother and more power. I'm always tinkering with timing etc but this has made a real difference.
In the old days I used to get 38MPG regularly on 3 star petrol, on modern petrol only 30-32 mpg and that's driving slower -as I'm a bit more sensible now.