I use both radios and my advice is to use the 817 in winter if there is any chance of moisture getting into the kit. Yes the KX2 is lighter (and more fragile) but seems to develop problems if it gets damp, not even wet! I also use a watertight 1120 peli case for the KX2 which is 3lbs in total, so no overall weight saving.
My choice might be influenced by our Scottish conditions in winter!