Hi BriExpat77,
 I hope you would decide to go to Islamabad since its more peaceful and healthy as compared to Karachi.
 Yes, I know many of my cousins, friends and colleagues studied from there and they are at best places and they got admission easily at Australia, Canada, Germany etc..
You can select schools based upon your budget. I wont say you must go to expensive schools only. There are average schools which provide high quality education as well. And believe me, schools doesn't matter a lot.
I know people who studied from Government schools, colleges and universities and they are British, American, Swedish national. All are my family members which I am talking aboutÂ
First confirm you plan for Islamabad. Then I will guide you through the locations and list of very good private schools as well.