Also, the instruction decode cases for 16bit mode is still in the main instruction decoder and not ucode AFAIK. They're almost the same encoding, and there's not enough ucode pace for it all, but removing those cases from the muxes there would help power consumption. Yes, you run out of the uOp cache a lot of the time, but not as much as you might think, and AFAIK the instruction decoder is still cranking away in the background because you want it to be immediately available as soon as an instruction is not in the uOP cache. That means the power efficiencies can be gained there.