2.92, Optix CPU + GPU is slower than GPU only

[YAFU]

@AlexisBenoit

I setup a quick test scene, a Nishita sky for the environment, a plane emitting 2500 icospheres as hair, and 100 interpolated children, with a standard principled shader.

What about other scenes?
BMW Demo:
https://download.blender.org/demo/test/BMW27_2.blend.zip

Classroom:
https://download.blender.org/demo/test/classroom.zip