0w20 only comes in synthetic.
5w20 can go dino or synthetic.

you will lose 1 mpg or so switching to the higher viscosity.

If you look or if there was one of those engines in a few years back before the mpg requirements went up, you will see it was 5w20 for that same engine.

they did it for mileage not because the engine needs it.

Since both have the same viscosity warmed up it doesn't matter.