Remember the 3G on iOS 4 fiasco? Why did that happen? The 3G was on a different architecture (ARMv6). iOS 4 was designed for ARMv7, 3GS and up. Because of this, the iPhone 3G was slow as a brick. Now with the A6 (ARMv7s), you can expect iOS 8 coming two years later to be a repeat of iOS 4. Pre-A6 devices will lag regardless of how fast it is or if it's a singlecore or dual core. It's because of a different architecture. This isn't like 3GS -> 4 which has like a 20% performance increase. This is double just by specs.