Thanks for the analysis. Reducing the triangle count in always beneficial for a Shapespark scene, as it improves the frame rate and shortens the load time. However, the the 500K limit may require significant quality tradeoff for larger scenes, and may be too restrictive for a rule of thumb in my opinion. An average Shapespark scene visitor is not a gamer, so I think, has some level of tolerance for a lag. Also, based on what we hear from our users, feature/quality improvements seem to be currently more important than frame rate. That’s, why I think 3-4M triangles is reasonable as a general rule of thumb.
That said, I am aware each case is different. If you anticipate your audience is sensitive to low frame rate, you can adjust the general rule of thumb to your use case.