@salik990 @tintin1 @naveedj53 @altisdualvvti
I have just finished reading the whole conversation.
Thanks a lot brothers for your time, patience and guidance and sharing your knowledge / experiences.
For some of my friends, 0w-20 is working flawlessly, for others 5w-20 is best (if 0w-20 can work flawlessly, then 0w-30 would be even better specially in summers, and 5w-30 ka to issue hi nai hai)
And we have at least one person for each 0w-20, 5w-20 and 5w-30 here, with personal experiences with these oil grades; and without damaging engine or compromising its integrity.
In a nutshell and as per my verdict: 
0w-20, 0w-30, 5w-20 and 5w-30 API SN, Fully Synthetic Motor oils are best suited for 660-1000cc used JDM vehicles and can even work throughout the year (but depending on cities, like Islamabad or Karachi and wise decision between these 04 grades)! And one should always choose and decide between these oil grades only, for 660-1000 cc JDM vehicles 
Once again Brothers, big bundle of thanks.
Jazak ALLAH and Stay Very Very Happy and Blessed!

Thank you.