Transparent animations vs faux transparencies?

Is there a difference in performance using an animation with the transparency set to 60 over a sprite vs an animation that appears to have a transparent object in it. Like water flowing over rocks...? I searched around but only found references to sprites using too much transparent areas.

Thanks

As I understand it, 100% opaque pixels are the fastest to render, fully transparent the second-fastest, and semi transparent third fastest. I don't think it matters whether the sprite's opacity is set to 60% or if the pixels contained in the image itself are 60% opaque, I think they will both render at the same speed. However, having an image where the actual pixels are rendered fully opaque but there appears to be a transparent object rendered in the image itself will be faster.

It also results in the video card having to draw less pixels, which is especially a help on mobile.

Thank you Arima!

"having an image where the actual pixels are rendered fully opaque but there appears to be a transparent object rendered in the image itself will be faster."

exactly the info I was looking for :)