Yes, EO affects FC
SAE30, viscosity is low hence it flows faster at cold start, better protection at areas where a higher viscosity oil takes longer time enter at ambient temp. Problem is that the molecules breaks down much earlier when heat is introduced. Hence those using SAE30 you will feel you car lose power at hot afternoon but engine is very lively at morning or at night time.
SAE40, is has a higher viscosity than SAE30, so at cold start the engine noise would be a bit higher due to engine oil is taking a bit longer to reach into small and tight areas, you need to use decibel meters to measure the engine noise not your ears. It can take more heat and maintain lubrication property compare to SAE30.
SAE50, has the highest viscosity but provide the best protection when the engine is hot can take in much more heat. For older car that makan minyak and can't afford to do overhaul, mechs usually recommends using SAE50 to avoid too much engine oil sipping through the piston ring and get burnt off in the combustion chamber.
If you see most turbo cars and race cars, they use SAE50 because of the extreme heat that those engine produced and the engine's rev are mostly rev to 8 ~10K.
For normal street driven cars, SAE40 is optimum while SAE30 will be good if you stay at Cameron highland or Genting or you drive your cars mostly at night or morning only. You can still opt to use SAE30 but in hot days the oil will lose some of it's lubricating properties. I have some friends who use SAE30 but they add in friction modifiers on each oil change.
Just my 2 cents.
Nice explanation....Anyway, I prefer SAE40...haha.....I think this is for common user~~~