I personally believe that for Vitz, Passo / Boon, most of the used JDMs, PKDM Atlas Honda vehicles, and even PKDM Toyota vehicles (although many will disagree), 5w-30 is the most balanced and most suitable engine oil grade throughout here in Pakistan for all season / all weather conditions.
I do not understand, why people pour thick oils unnecessarily in brand new engines with latest tech., which will be used in normal driving conditions? (Drag racing / racing, and extreme loading conditions to be precise, for abnormal conditions)
Pakistan is not some out of this universe country with severe / extreme weather conditions, dusty environment, bad quality of fuel, etc. Some regions are even more worse, and even in USA too (Arizona, Death Valley, Texas, etc. To be precise). Extremely hot and 5w-30 is being poured in the engines since years. Some have even clocked more than 3-5 lac Kms without any major / minor engine overhaul. And humidity, bad quality fuel issues are there too.