I also think you are making a mistake by excluding carbon bikes because you are afraid they might break, especially if your primary goal is long distance, comfortable riding. Carbon is probably exactly what you are looking for. I have 20,000 very comfortable miles on my current carbon bike and it hasn't broke yet.
The Cannondale Synapse is a pretty good suggestion for the upper end of your price range (there are several good choices). If I was going on a century ride and if I had to choose between a CAAD9 and a Synapse Carbon, it would be a no-brainer and I have spent lots of time on a CAAD9.