anexanhume
Veteran
When following Apple's design cadence it's consistent that the CPU/GPU improvements in the A8 are more modest, after-all it's the "s" iPhone refreshes that focus on speed. The iPhone 3G used the same SoC as the original iPhone with no performance improvements. The iPhone 4 A4 used the same CPU/GPU architecture as the iPhone 3GS and was only up to 50% faster despite having 4x the pixels so it's probably the most comparable. The iPhone 5 A6 is the exception with 2x faster CPU and GPU, but the GPU was the same PowerVR Series 5XT architecture as the iPhone 4s A5, so no new features, just faster. The A8 does move to a different architecture, the Series 6XT with new features, a transition that previously only occurred in iPhone "s" refreshes, but the raw performance increase is a more modest 50%.
FWIW, Apple had been claiming 2x CPU improvement every generation from A4 to A5 and on until now. A5 did it with dual cores and OoO. A6 did it with a big clock boost and wider design. A7 did it with even wider design and ISA jump. This time they simply couldn't go wider efficiently and clock boost seems out of character with their power/speed balance historically.
Is it possible that all A8s for the iPhone are manufactured by TSMC and the A8s claimed to be made by Samsung are actually for the rumored iPad Air update later this year, and are somewhat different from the iPhone A8s? 40% seems too much for an iPad-only chip though.
It helps in terms of schedule by a few months at most, so I don't see it as a huge advantage. It will be interesting to see if they have the same GPU as seen in A7, though.