Below is just to share my good experience with Caltex Havoline Fully Synthetic SAE 5W-40.
I had imported Vitz 2007 1.0L in August 2012 with genuine 7000Km on ODO. Drove it fine on the Japanese petrol and engine oil before taking it to Toyota Defence Motors in DHA Karachi. Those fools poured in the locally blended Toyota 20W50 and the drive changed drastically. After going through its user manual (in Japanese) and doing some research I immediately switched to Caltex Havoline Fully Synthetic SAE 5W-40 (Golden packing). It has been more than 2 years, ODO now shows more than 31,000 and the engine is going super fine in terms of sound, oil level, fuel consumption and no deposits inside. I change the oil at around 5-6,000 km interval.
From the beginning there is rare (like on speed breakers etc) and very slight knocking sound on regular petrol that too only with AC turned on which completely goes away on mixing a little Hi Octane.