Consider Compound vs BigCompound heuristic helper

[RossNordby]

It's not immediately clear to many users whether they should use a Compound or a BigCompound. That's understandable, considering there is no fixed threshold of child count. A better heuristic would examine the SAH of the BigCompound tree versus the brute force testing of Compound.

It would require building a tree, but this kind of choice can be made offline.

Possibly worth a demo? Or an expansion of the CompoundDemo?