ADDED: There are also singers with a 5-octave range — 28 of them! — including Axl Rose.
But "The page 'Singers with a six-octave vocal range' does not exist." All right then. There are limits!
NO. WAIT. There is a Wikipedia category "Singers with a six-octave or greater vocal range." There are 6 names.
On that list is Georgia Brown...
... pseudonym of Rossana Monti (born June 29, 1980) is an Italian Brazilian singer noted for her extensive vocal range. She was listed in the 2005 Guinness World Records for hitting the highest vocal note and for possessing the greatest vocal range for a female, claimed to be exactly 8 octaves from G2-G10 using scientific pitch notation. However, as of 2013, Tim Storms holds the record for the widest vocal range of any human with 10 octaves.