Most eugenia are ok down to 32f - some lower - but I wouldn't gamble on it. Other than involcrata, all my eugenia suffer and drop all their leaves during 9b winter if I leave them outside. They get REAL ugly if it drops below 25f and you'll get severe branch die back.
Langsdorfii is a cerrado species. The lowest the cerrado gets is 50f.
Because Langsdorfii seeds are so cheap I would risk it and let us know.