Then both Mira and Passo suits your needs.
If you have a lot of long trips, then consider Passo.
If long trips are seldom, then Mira will do the purpose too.
I have just taken 660cc a couple of time on long route (ISB-LHR) motorway (about 450km), no stop is required even in summers if you have reliable tyres.
and i have taken Passo many times on Motorway, it gives best results.
about mileage on long routes using a 660cc, if you travel at 60-90 km/h then it will give you better mileage like 23-27 km/ltr.
but if you drive it at 120km/h speed, then mileage is about 14km/ltr