I would like to share my observations on 3 motor oils. All data were collected with a least 7 full tanks of fuel. I drive the same route everyday and have pretty similar traffic conditions. The way I compute my FC is by recording the amount of fuel that was required to fill my tank, then divide it over the distance I covered.

Mitsubishi Turbo XP "Fully Synthetic" (Group III)
-535km/full tank or 8.9km/L

Mitsubishi Mineral Oil (Group II)
-500km/full tank or 8.3km/L

Royal Purple HPS (Group IV)
-600km/full tank or 10km/L

Haven't computed yet the correction factor since i'm using slightly bigger tires than stock. Im using GLS wheels and tires on a GLX model Strada.