AnandTech has dug up some apparent benchmarks for the iPhone 4S, which they found around different benchmarking sites and believe to be true. Judging from the numbers, it seems like it'll be one of the most powerful mobile devices around.
Overall, these early benchmarks show the iPhone 4S is less powerful than the iPad 2. But it's superior to every other smartphone—the Samsung Galaxy S II and the Motorola Droid Bionic being the best of the bunch— and equal to Samsung's Galaxy Tab 8.9.
In terms of hardware, AnandTech has determined that Apple is underclocking the A5 chipset to ~800MHz and running a slower GPU than the iPad 2. And in case you're wondering why Apple likes to underclock their chips here's why:
A lower clock not only means higher yields from the factory, but likely a lower operating voltage as well. Dropping a CPU's core voltage, yields a greater-than-linear decrease in power consumption, making the marginal loss in clock speed a good choice. At a lower operating frequency than its Android competitors, Apple does have to exploit its strengths in software to avoid any tangible performance penalties. Apple has traditionally done this very well in the past, so I don't expect the loss of frequency to be a huge deal to the few who do cross-shop iOS and Android.
Even with the rumored 512MB of RAM, the iPhone 4S is shaping up to be a beast. [AnandTech]