I reached Gujranwala from Isb in 2 hours 45 mins :). Almost same time on return.
I only gave way to one car, a zero meter Civic. Overtook many Altis, Xli's and even a Prado from left (I'm a bad driver who doesn't bother to flash the headlight 2nd time). But good thing is, I kept it constant at 100~110 most of the time.
Now the funny thing. My cousin was heading to same destination in his 2004 alto. He maintained a speed of 80Km/h throughout to achieve good economy. Results:
Alto consumed Rs. 6000/- worth of petrol for the return trip
Nissan filled only Rs. 4500/- petrol and happily came back. (And I'm not sure how much petrol left, that stupid gauge and stupid owner :P)
It will take some time to update on the average on long route. My guess is around 17~18 min, when that alto gave 11 kpl.