The battle between ARM and x86 (Intel) has been gaining steam more and more lately as Intel begins its movement into the mobile space (tablets, smartphones, etc.). Here is an article that provides a detailed analysis of ARM vs x86 in regards to performance and power consumption. Surprisingly, the paper  concludes that the current Atom processor and the ARM Cortex A9 are mostly equivalent at the current moment.

A Detailed Analysis of Contemporary ARM and x86 Architectures (University of Wisconsin - Emily Blem, Jaikrishnan Menon, and Karthikeyan Sankaralingam)