Farhansa,
All lubricants available in the world are same and varies only by their API & SAE. Companies in Pakistan have almost same API grades lubricants available, either its Shell, PSO or Caltex. Higher the API means better performance. SAE 20W50 & 15W40 are fine for Pakistani weather. Secondly it depends on your car & model. Using higher API grade in old cars won't serve the purpose. API SG grade lubricants can be used upto 5000 Kms easily. But also use genuine filters.