Guys better then Posey - Josh Childress, Luol Deng, Bonzi Wells, Iggy,
Equivalent to slightly inferior - Matt Barnes, Quinton Ross, Mo Evans, Ricky Davis, Delfino, CJ Miles.
To start with ... Josh Childress, Luol Deng, and Andre Iguadola are restricted free agents and the chance that their team doesn't match at the MLE is about the same as Roseanne Barr appearing in a Victoria Secrets catalog. Why even bring them up? It is kind of like the Corey Maggette fallacy.
Now, let's go over your list
NOBonzi Wells - Have you watched a basketball game in the past two years? Wells has regressed badly and has a reputation of being in bad shape/a cancer. He does atleast try on defense, but gets exposed badly by anyone with a decent first step.
Matt Barnes - Tweener PF/SF whose slow feet makes him a poor defensive player. Plus, he has a history of bad turnover problems. He was useful in Don Nelson's system, but is a poor fit for this one.
Quentin Ross - Nice defender, great athlete. Now if we can overcome the lack of any offensive game. The guy is basically as close to useless on the offensive side of the ball.
MAYBERicky Davis - OK ... now we got a player in the same category of talent. IMO, probably a more complete offensive talent. That said, he is a cancer that has been on several teams and his defensive effort is seriously questionable
Mo Evans - No ball handling skills with a decent outside shot. Unfortunately, a very limited inside game and not a finisher at all. Of the names you mentioned, he might be the best of a weak group.
Carlos Delfino - OK I like his defense, but his lack of an outside shot hurts.
C.J. Miles - Liked his improvement in year 3 and looks like a nice young player who wants to return to Utah.