there is not much difference with and without AC,
as summer has just came, i have just used AC upto first or second Fan speed. but not fully utilized AC yet.
without AC, mileage of my Passo (with original tyres) was 17-18 km/ltr (all mixed including highway, rushy areas, small roads, rough roads, where brakes are often applied)
but with bigger tyres (185/70/13), it dropped about 1-2 km/ltr