It's been more than 500 days since Stanley Cheslock put his Greenwich (Conn.) mansion up for sale. It's one of 52 priced at $10 million and above on the market in the hedge fund capital about 30 miles northeast of New York City, the biggest backlog since at least 2004, according to Mark Pruner, an agent with Prudential Connecticut Realty. Four in that range have sold this year, and two are in contract.