3) Using the external brightness setting (IBL) (to some extent). TRUE Sample values have been increased for good interior rendering and better definition of the outer shadows.

It's a very nice feature that I use a lot.
Adding different colours or images (or even solid black) to the top part of the sky, can really make some incredible lighting effects.

And I'll add in 4) Using detailed or complex objects like trees. In this case, the rendering "stagnates" on a part then accelerates.

Absolutely!
But it's important to differentiate between large and complex models.

C