CSS Sprites vs. Data URIs: Which is faster on mobile?

I'd be curious as to the underlying why here.

I imagine that CSS parsers aren't particularly designed with any kind of parallel operation, whereas grabbing images (& decoding them) is largely done in parallel (up to the number of max connections). So while you're parsing the CSS you can be getting the images, offsetting the connection cost.

In the CSS case, the device needs to get the (slightly larger) CSS, un-gzip it (with more complex tables), Base64 decode - and then decode the image as before. I wouldn't be surprised if this is a completely sequential activity with the rest of the CSS parsing.

I have the same question as Jochem Bökkers and Anil Namde had in the comments - why wouldn't you use both? I'm sure there's a good answer, but I don't understand.

I must have missed the Data URI hype, because I'm not at all shocked that CSS spriting is faster than using Data URI. We are comparing using a binary image format, and a base64 encoded image inlined into CSS/HTML.

What isthe basis or the source of the idea that base64 encoded images inlined into the CSS would be faster?