Mobile bandwidth is somewhat of a red herring. While ubiquitous 4G isn't reality, most smartphones and networks are already capable of fairly high bandwidth.

Latency is the bottleneck you should tackle first when addressing mobile performance, not asset size - the world has already spent a lot of time optimizing asset size for web delivery. But phones are bad at handling lots of requests. Serving a single high-resolution graphic will have significantly less impact on page rendering speed (and even more important, perceived rendering speed) than a handful of smaller assets which add up to the same size.

For a real world example, a mobile phone can download and render a single large photo faster than the gaggle of javascript, css, and social network share icons typically presented next to it.

Many have examined and written about this. Here's a blog article that Google ranks on the subject: http://www.webperformancetoday.com/2012/04/02/mobile-versus-...