Core M behaves a lot like mobile SoCs in that it aggressively down-clocks when idle to be efficient and ramps up under load. Once you understand that, the CPU differentiation is a gimmick to milk money out of consumers. The point of Core M is efficiency so the model that can be more efficient when idle should really have more of a premium. Turbo clock is another gimmick since you'll unlikely see max clocks with all cores under load and there's also the question of throttling under sustained load. From what's seen so far 5Y10 doesn't throttle while 5Y70 with active fan does throttle under sustained load. rMacbook 1.2/2.6GHz option which is similar to 5Y70 is highly suspect of throttling considering it's fanless. The other 1.1/2.4GHz option might fare better and the one I personally would go with.