Spark overhead

[Shadowstar]

Just out of curiosity, does anyone know what the processing overhead is like for a spark emitter as opposed to a sprite emitter? I would think sparks would be much easier since they are just a single pixel. But I'm wondering if perhaps the difference could be expressed as a ratio? Some effects I'm considering could use spark emitters to great effect, but would need to render many particles to be effective, and I'm wondering how many particles I could get away with rendering before the FPS starts to take a hit.