I had a 2009 addict SL and I sold it for those exact reasons, its just not a very vertically compliant frame. My 54 weighed 808g so I was very pleased in that respect but I just didn't feel the love.
I do not own one, but have ridden many models, the Cannondale Evo is next on my list. Its most defiantly more comfortable then my addict and I feel it has similar torsional (I'm 150 lbs) stiffness while being around the same weight.
I surely wouldn't put down the money for a Z5 when Evos now retail for $4000 for a Sram red complete bike but that's just me.
I want to build it up myself, so I'm looking for frame/fork. I think I could get a "like new" EVO right now for around $1500. The Parlee is 2012 new @ $2500. I'm a little concerned about fit, but I have 30mm of headset spacer on my Addict, and that's why I'm thinking the M/L Parlee would be nice. The EVO in medium is pretty darn close to the Addict so not really a problem.
BTW, I do still really love my Addict, but if I was to fix something, it would be the vertical compliance. I could just upgrade it to DA 9000, and sell the 7800, but I think I could sell the Addict as a whole bike easier than parting out the components, and maybe get an equal performance, yet slightly more compliant frame too (okay, and little extra money).