You know, I had a thought: Shiva would be fine for a warm, romantic component that needed some speed, but not for components that are lean, mean, fighting machines already. In such an instance, it seems to "lighten" the presentation. Besides all this, the Vishnu has much more airiness, "aliveness" and nuance than the Shiva, which, to my ears, has very little of those particular traits.
Shiva is Paris Hilton: Vishnu is Diana Rigg.