Despite the current processor performance focus in the smartphone space, Apple keeps quiet on the architecture of its new chips.
However, Nomura Equity Research said that the A6 chip in the recently unveiled is a Cortex-A15 design manufactured in a 32 nm HKMG process by Samsung. There was no information on the clock speed, but we know that the Cortex-A15 in the dual-core Samsung Exynos 5250 currently scales to about 1.5 GHz in smartphone applications.
Apple itself declined to comment on the statement and referred to its press release, in which the company describes the processor as "blazing fast" and "designed […] to maximize performance and power efficiency to support all the incredible new features in iPhone 5, including the stunning new 4-inch Retina display—all while delivering even better battery life." According to Apple, the A6 has "twice the CPU and graphics performance" of the preceding Cortex-A9-based ARM chip.
Apple still licenses the graphics IP from Imagination Technologies, which would make it reasonable to assume that the A6 uses Imagination technology as its graphics engine. Details are unclear, even if we tend to believe that the A6 still uses a PowerVR series 5 chip than a version of the PowerVR series 6 (which has not been formally announced, but is still believed to debut sometime later this year). According to Imagination, the series 6 chip is much more power-efficient than the current series 5.