Evidence found in the iOS 4.3 firmware just released today reveals that the iPhone 5 will likely get the same A5 dual core processor used in the iPad 2.
@chronic found that the A5 processor is called S5L8940.
iPad2,1 (K93AP) = WiFi. iPad2,2 (K94AP) = GSM. iPad2,3 (K95AP) = CDMA. all run on the S5L8940 proc.
@FilippoBiga then posted the image below showing that the iPhone 5 (N94AP) kernelcache.release file contains references to this same S5L8940 processor.
Heres the proof, iPhone 5 will run on the S5L8940 (A5 dual core processor) too!
It's not much of a stretch to believe that the iPhone 5 will use the A5 processor just like the iPhone 4 used the A4 processor after its debut in the iPad; however, now there is some evidence to support the assumption.
Click the picture to see it clearly