The route is similar to yours, Islamabad, motorway to burhan interchange, haripur, abbotabad, mansehra bypass, balakot kaghan n Naran.
Firsly I have been there a few time over last few years so know the way pretty well, so no time wasted there. Motorway speed hardly 110kmph. Rest of the roads, speed depended upon condition. We left early (5 am), so were in Abbotabad before 7, and probably mansehra bypass well before 8, so missed most traffic. Being on NPP means high road clearance and so quite possibly the bumpy / broken down road does not slow us down as much as if we were travelling on the car. Overall our pace could be called moderately brisk and no more. No crazy overtaking or speed testing etc. I did similar timings last year as well......both ways, details on top of the page with the link to our other trip thread. And finally we hardly ever stopped, only fuel/ toilet stop at Balakot both ways.
Suhaib may have a different version to tell though!
BTW the return journey timings were not too flattering due to immence traffic.