In Fantasia Impromptu (an Underworld Amusements edition slated for release later this year), Benjamin makes the following note:

George Sterling.—George committed suicide at fifty-seven. The perfect age for poets to pass. He took a quick curtain instead of a slow one.
A charming man, a “regular” fellow, a bohemian of the old school. I received a letter two weeks before he died which was full of hopes and projects—one was an article on Bierce, another was his intention to visit New York. But the Imp of the Perverse suddenly reversed gear on him. He had not received his copy of “The Sublime Boy” up until two weeks before his death. But he had got it, unquestionably, before he committed suicide. A thought has come to me that the story of Walter’s death may have influenced him.

George Sterling (wikipedia link) reviewed Forty Immortals. That review can be found on the books page.