^^
IMO, upper range of oils should not be less than 40 keeping in view weather of Pakistan. we can have some variation in lower limit though. So recommended grades would be
5W40
0W40
and 10W40.
I found a useful writing on multi grade oil at this link, which i am pasting below
In a nutshell, the 2 numbers represent cold start (the number before the 'W') and the 2nd number is for warmed up running conditions.
The numbers basically represent viscosity. The 2 numbers are basically 2 different viscosity oils in one (synthetic). In colder climates you want lower numbers so the engine is not damaged if the oil is not warm. In this case 0 or 5 is warranted. In warmer climates you can go up to 10 or even 15. The creation of these synthetic oils is the reason newer cars don't need a warm up period and you can just start and go. The oil is already slick enough to run on a cold engine. The problem is the warmer the engine gets, the lower the viscosity (the numbers) get and basically you can have viscosity breakdown which can lead to engine damage. Thats where the 2nd number comes in play.
The second number basically represents viscosity at normal operating temperature. It's the 2nd part of synthetic oil that protects your engine when the car is warm. 40 is generally good for all around use. 30 is also good but not recommend for extended driving, because remember what happens over time is the engine gets warmer and the oils viscosity can breakdown (eg. a 40 grade oil can become a 30, a 30 grade oil can become a 20, etc). 40 is good overall. If you notice in race engines, which can become very hot they use much higher viscosity oils (eg 15w50 or 15w60). This is to prevent breakdown of the oil in high temps.
Thats it in a nutshell. Basically first number is for cold, second is for operating temp. Lower numbers for lower temps, higher numbers for higher temps.