That being said, I did notice a huge difference in the snappiness of the javascript code as opposed to events. It felt like a completely different engine and I had never felt that kind of responsiveness from this engine before.
I tested two templates for Ghost Shooter (event-based and JS-based), and noticed no difference. As others have mentioned, events in C3 are interpreted to JS, so for most of them there shouldn't be any difference whatsoever.
In other words, re-creating functionality of C3 standard plugins and behaviors with JS would be a waste of time, because the engine already does this for you.
I only use JS when I need features that don't exist in C3, or when processing huge arrays, for example image data of a large drawing canvas.