Point here is to say that 5w30 is also perfectly fine and also can be used and is recommended by toyota and the same goes for 0w20.
But point is to inform the guy that if he wants to use 5w30 as long as it is recommended and written on manual he can with no issues. And if he wants to use 0w20 thats perfectly fine as well, no issues with that.
Also "optimum" efficiency can easily be achieved with xW30 oils also, its "maximum efficiency" which is achieved using the lowest grade oil which is recommended.
Difference in efficiency between xW20 and xW30 is minimal and not have major difference on fuel economy. Again, im not against using xw20 oils im just saying that xW30 is perfectly fine so long as its recommended in owners manual