Zhob to D I Khan is 225 kms and the road is just fine if not very good. It took me little over 3 hours to complete that section. It gets very interesting in the area of Danasar where it enters the Suleman range.
Then I think this is the shortest route for Quetta for people in ISB/RWP. Hows the security situation there?
I didnt face any problem there apart from D I Khan trouble I mentioned. But people try to avoid this route due to its proximity to Waziristan and the situation in DI Khan but I think it is not that bad and u r right about this being the shortest route.