"There's a lot of nonsense here. The ARM instruction set IS more efficient, for people who understand technology, instead of repeat what they hear from their Intel reps.
There's no question about this. A quick class in microprocessor design will make this clear enough The question is only, does it make enough of a difference. It's not big enough to make other advantages irrelevant, and is certainly less of a disadvantage than having a superior manufacturing technology is, in this case. But, it's still a disadvantage, just not a salient one in today's world. As other things equalize, if they do, it will be more of an issue. Right now, it's a quite minor consideration.
The power/efficiency is pretty good, but the IPC is poor. It struggles to compete with Kabini in CPU, winning some, losing others, despite being able to turbo boost from the base 1.5 GHz both run at, all the way up to 2.4 GHz(the tested Kabini was stuck at 1.5 Ghz). IPC is markedly inferior. Forget the GPU, it gets annihilated completely. It's a complete blowout there.
Not that this is necessarily bad. Intel can't do graphics. They don't know how. Not smart enough. They try, they fail, they embarrass themselves. Better to spend their watts on CPUs, which they do know how to make quite well.
Bay Trail isn't a success, really. It's not bad either. It's disappointing, but only in a minor way. Power use is good, but not crazy good like Intel was boasting, IPC is fairly horrible, especially when compared to Kabini, and the GPU is miserable. But, taken together, as a sum of all parts, it's got nice CPU performance for the watts, and can still be very attractive in devices that don't need a strong GPU.
The problem is the same as Haswell - Intel built it up too much. I was expecting a much stronger GPU. It's surprising how poor it is, as a newly released product and with all the talk from Intel, but it's still functional in many scenarios...
Kabini is in Haswell's power consumption class not Bay Trail and so Bay Trail will last 50-100% longer on the same battery yet Bay Trail is in same cpu performance class. I am not convinced anyone buys tablets as a gaming device so as long as the gpu can power the chosen screen resolution that's the job done but just in case Haswell-Y has both better cpu and gpu than Kabini in the same power class. When Airmont arrives Intel will close this gpu gap and Kabini will have nowhere to go but extinction. Semi is right, Silvermont is the new T-34 of the mobile world and it will knock out all the inefficient ARM/AMD panzers it faces.