I think comparing oils and their qualities is like comparing hammers of similar weight... different packaging... but it's still a hammer and it hits the nails. :)

I was reading an extremely detailed article about oil (though it's in russian: Honda Jazz Club • ?????. ????? ?????? ?? ??????? ????? ???? ?? ???)

and saw an interesting factor that will depend on the viscosity of oil.
The article said that the majority of heat from the combustion gasses is dissipated by the piston rings (they claim it's btwn 60-80%), at the same time the heat transfer characteristics of oil is very low. The thicker the oil film, the less heat is taken away from the piston. (higher viscosity oils like 5W30 will leave thicker layers of film than let's say 5W20). So since the less heat is dissipated through the rings with the thicker oil, the more the piston expands and starts to scratch (act as an abrasive) on the cylinder walls. This wears out the cylinder walls faster.

So, the bottom line, there are a whole lot of reasons why specific oils are recommended to specific engines. This is why I will personally chose the Honda recommended 5W20.

It would only be on the power stroke when the pressure between the rings and cylinder that the film strength of the oil increases that heat is retained and there is less pressure during the exhaust, intake and compression strokes where there is less pressure and the oil flows freely doing its job of cooling and lubricating.... The film strength of modern synthetics increase in film strength under pressure irrespective of weights..... It is only in the North American market that manufacturers recommend 5W20 oil to meet the legislated fuel mileage goals set on manufacturers..... 5W20 is non existent elsewhere in the world.... I have used nothing but 5W20 in the vehicles we drive since 1997 with out any problems but I will change to 5W30 in my Fit at the time of my next oil change as a precautionary measure to protect my engine from the additional heat from an upcoming series of power enhancing modifications and the high temperatures of summer driving..... I have no problem at all with using even 0w20 for summer driving in a stock FIT as long as it is a synthetic type oil.

The Definitive Skinny on Oil
 

Bottom Line. Use 0W20 or 0W30

0w-20 Vs 5w-30 Oil (which Is Better For A Chevy) - Vehicle Appearance, Care, & Maintenance - GM-Trucks.com

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