My view is that the viscosity of oil depends on the temperature range in which the engine operates. There is a lot of difference between the weather of cold country and hot country. In a cold country the oil in winters may literally be frozen solid, i.e. difficult to circulate in the engine when engine is cold.
Therefore 0W20 or 0W30 type oils are not suitable for conventional gasoline engines in Pakistan. They may be ok for Hybrids, as hybrid engines operate differently as compared to conventional gasoline engines.
For Pakistan for a non hybrid gasoline engine I would recommend (and the local manufacturers also recommend) 5W30 or 5W40. If the engine is very old and is about to come apart, then it is a different ball game. But 20W50 is the worst thing you can put in your engine unless the engine is about to come apart.
The first no. is very important i.e. 5 in 5W30. This no. determines how quickly the engine will be lubricated in cold start. Remember max. damage/wear to engine is done in cold start. The 2nd no. is important, but not so important. It simply increases the viscosity when the engine is running hot. However a running engine in any case has minimal wear. The wear has already taken place at starting time.