I physically picked up a 2015 7.4 FX size 17" at a Trek dealer a few days ago to see how heavily it was and I was shocked at how light it was.
From putting together bits and pieces of what I've read, I suspect it was probably around 23 pounds, and if so, I struggle to imagine how light a 16 pound bike would feel.
If anyone has actual weights of their FX, I'd be keen to see them posted in this thread.