Option 3. Long battery life running thinks at an OK speed.
Well, that's fine, but Intel have come on leaps and bounds on power consumption these past few years (spurred / scared on, I expect by ARM). Surely a small, native implementation of x86 (looking at you, Atom) could be created more efficiently than ARM running an emulator (albeit on in hardware).
Or course, my understanding it that the current x86/x64 chips decode the instructions into smaller chunks, and that the native silicon actually runs a simplified instruction set. I could well be wrong on that (CPU design is not my thing), but that would suggest to me that even Xeons are running "emulated" x86.
And yes, that was a fair few brackets I used there - not even sorry. :P