In continuation to this, today I filled pso hi octane and drove the exact same way coming from isl to Lahore and got 15.9kmpl. And this was with an extra passenger and slightly less luggage than before. So 0.6kmpl better with hi octane on motorway, but with the 26rs difference between hi octane and super, I didn't break even. Approx 400rs extra was spent getting hi octane for about 400kms.
If the difference was 10rs, then break even would've been achieved. At above 15rs difference, don't think hi octane is worth it for 1.5 CVT.