I'm the happy owner of 2 pairs of Castelli Free Aero Race Bibs and a Sugoi RSE Bib, Castelli Ergo Tre shorts & PI microsensor shorts. These are the best shorts I've worn.
The chamois is the same Progetto x2 as the Free bibs, so the only difference is in the short/strap areas. You have to be careful to get the correct size in Castelli: they make everything at least one size smaller than anyone else, so go to a cycle shop and try it on before ordering online!
I have no beef with the straps, in fact prefer them to the Free straps, although just a bit. But man, what a difference in the one-piece construction short! I don't know how they did it, but it hugs every point of contact throughout the entire range of motion, and stays in place,, with no chafe, rub or bind. They're criminally expensive, but they get cheaper every mile of a century: believe it!