Long debate. Appropriate forum is the lubricant discussion forum. Moreover this debate happens across all car/oil forums and never ends.
In short, 0w20 is absolutely fine for R18 and used globally. "warm climate so go Gaarha THICK oil" is old thinking, not applicable since the invention of multi-grade fully synthetic lubricants. They work excellent across all temperature ranges, 0w20 is used in the deserts of USA and Australia (much hotter than Pakistan).
It will provide slightly better fuel economy than a 5w30 and the engine will also love you for the good lubrication.
Cannot go wrong with 5w30 either, that is also absolutely fine and provides good lubrication and protection. Not as thick as a w40 or w50 oil, which are a NO-GO.
My issue is only when people come and say don't use 0w20 as we have "warm climate" and it is "too thin". That is not true.