for car above 100k you should use 10w-30, for high rev engine usually is -40, usually motorcycle is at 10w-40 as normal 10w-50 is for those who likes to rev at 10k rpm and above. most normal cars usually go at 2k-4k rpm, so stick to your manufacturers recommendation. Those that like to rev at 6k till max depending on high performance engine every other weekend, better go with 5w-40. At high rpm 5w-30 won't offer any protection
To be frank, my 10 experience tells me, that in Malaysia, our car should use 10W50 engine oil ideally, my digital temperature sensor installed read 70 degrees C, however, with 5W40 grade, the temperature read 82 degrees C, and used a 15W50 engine oil, the temperature read at 62 degrees C, engine power feels very very slightly less. And car engine's bonnet hand feels cool, however, using the 5W40 engine oil, the car engine's bonnet hand feels very very warm!!! Long term the bonnet paint faded over 6~7 years!!! Also, the high temperature under the car bonnet created a lot of issues, such as engine gaskets degraded, battery life shortened, and many other parts degrading too!!!