Anandtech and Chipworks deconstructed an Apple A8 processor, the hear of the new iPhone 6. By their analysis it is not a radical departure from the A7. It includes a slightly upgrade, but still quad-core, GPU, and an enhanced dual core ARM processor. The focus here is clearly on battery performance rather then sheer speed. Perhaps most interesting is the move from Samsung’s 28nm process to TSMC’s 20nm process (Being made by TSMC will hopefully put to rest the rumors of an Apple/Intel tie up once and for all.). This results in lower power, a smaller die area, and, assuming yields are on par, a lower cost per chip. Clock speed appears to be close to the same as the A7 at around 1.3GHz, with most performance improvements being architectural. It would appear to be the smallest improvement in the Apple A series, certainly since the A4->A5.
Considering the incremental improvement from the A7, one can only imagine what Apple has in mind for the A9 which is no doubt well under development.