Islamabad to Gilgit Tour.
Buy a GS150 if you will be touring in higher altitude areas or doing long tours. As all these guys said, you will have to take some pain for maintenance of GS150. If you keep it fit, it will keep you happy.
CG125 (2012 onward models) disadvantages will be, Suffocation on higher altitudes, bad shocks, bad tyres, bad comfort. You'll easily find the mechanic though.