10w-30 is the specced viscosity for the oil of a new Honda engine. If you are confident that your engine is not worn to larger clearances, then 10w-30 is fine. But since you do not know the history of the engine and it has been using 20w-50, going down 2 steps is asking for trouble. Why go for 10w-30 and then having to put the car in the workshop to fix up problems when you can step down 1 step to 10w-40 which is already very good even with regards to power and fuel consumption? The difference in power between 10w-30 and 10w-40 is not worth the headaches that you risk getting if you experience problems because the oil is too thin.

Just use 10w-40 for this oil change and if you don't experience consumption, then go to 10w-30 for the next oil change. It's not like you are just keeping the car for 6 months and have to use 10w-30.