Faisal bhai thanks for sharing your experience. I ll definitely give a try to this Rs1000 high octane trick and will post the my experience.
As far as oil grade is concerned, i agree 5w30 is the most recommended oil for vitz. Few months ago, i also did some research on it and finally get 5w30 is the best for vitz. But as i m in Lahore, and here temperature rises to 45 C easily, and goes to 50 C in peak times. So my findings are, 45C outside + engine heat, rises the temperature to very high level easily. We need different grade oil for summers, so in winters i used 5w30 and for summers i opted 5w40. Believe me the difference is noticeable, after pouring 5w40 car is smooth and accelerate very easily with AC. Do try it.
I m not using any High Octane right now, filling the whole tank only and only from Attock Pump located in liberty, their fuel quality is very high, perfect for JDM cars, i didn't feel any kind of knocking from their fuel. Give it a try as well.