At present, 2.3 GHz achieved at 28nm is the fastest clock speed by a mobile processor - it is used in the Snapdragon 800 and Tegra 4i that are set to arrive in late 2013 or early 2014. However, the next generation processors are expected to surpass this clock speed with the help of much smaller manufacturer node of 20nm.
The 20nm manufacturing node is expected to yield 30% faster clock speed with 1.9 times better density at 25% less power consumption. If the 20nm node is used, the ARM SoCs will be eventually clocked at 3GHz with more transistors working on the graphics. The 25% lesser power consumption can be potentially translated into a better battery life in the next generation SoCs.
Source: GSMArena
