My mom met and heard Rachmaninov when she was studying music in Chicago in the 30s. She said he had enormous hands.
In 1936 Rachmaninov came to Philly for the same program except that Eugene Ormandy had replaced Stokowski as Music Director. My mother was allowed to go to that concert, and she said the same thing: Sergei had the biggest hands she had ever seen on a man. She also said his manner at the piano was businesslike. He and Ormandy would occasionally glance at each other to be sure the orchestral cues were in the right place, and he wasn't flamboyant at the piano.
His version of "The Star Spangled Banner" was a reaction to Josef Hoffmann's bombastic version. I've played the Hoffmann arrangement, and you can hear the bombs bursting in midair. Rachmaninov wanted something more contemplative and thankful.
Three weeks before his death in 1943 from cancer, Rachmaninov became an American citizen as his final act of defiance of Stalin.