There is a comment from @jon_eg about this in this thread , I am copying it here:
“This will be addressed in the release. SM6 uses a new shader back-end from Microsoft that has more verbose instructions for the same level of shader complexity as SM5. A change went in after Preview 2 that will apply a rough multiplier to make the SM6 numbers look more like SM5. This will generally fix the shader complexity viewmode, but there will still be differences from SM5 instruction counts. SM6 instruction counts should only be compared to other SM6-compiled shaders.”