Just a little note -
This does not apply to the Nexus or the Google Experience versions of the HTC One or SGS4 - but -
The stock One and SGS4 each have a lot of extra software features, pretty cool and fair enough.
Those features take processing power. The Snapdragon 600 quad core handles them very well.
This phone has some unique whiz-bang features too - and X8, while only a dual cpu core, has separate, low-power cores to deal with those features.
Something the Snapdragon 600 lacks.