It's faster in single threaded tasks, but there are a few highly parallel benchmarks the A7 is slower on. Since Apple gimps RAM the A7's two core disadvantage is accentuated.
Once some of the latest Android designs hit the market in the next year, they will CRUSH the iPhone in performance. Think about quad cores running in excess of 2GHz. There will even be octocore Android devices.
My theory (more like WAG) is that Apple focused more on efficiency for the A8 so as to avoid a marketing problem with the A8 having higher performance than a quad core A9 in some instances. In a quad core A9, each core will likely have to be slower than the A8 cores if efficiency is to be maintained and the same 20nm process is used.
Whatever Apple's roadmap proves to be, it leans towards effiecency in lieu of performance due to the puny battery capacities imposed by Ive's design anorexia. Android devices will reign in both performance and battery life since they are content with "thin enough".