That is the fundamental question. If it remains in suspension and doesn't clump, can it cause any wear in the engine?

We all figure that soot is abrasive, but, there's no proof that the size of the particles can have an ill effect if they don't clump together.

One of these days I might run the Rotella syn to 8K or so and see how high the iron levels will rise. Is it proportional to mileage, or disproportional? That would be the only way to determine if additional soot levels cause increased wear.