On October 14, 1950, Efstathiadis broke the 15-year old Greek record of Panagiotis Chlentzos, jumping 4.03m. On May 4, 1952, he improved it to 4.055. Seven days later, he improved it to 4.17m in a meeting against Yugoslavia. He broke it once more (4.21m) on June 15, 1952.
Efstathiadis won gold medals in the Balkan Games of 1955 and 1957, both times with performances of 4.10m. He also had a gold medal in the Mediterranean Games of 1959. He participated in the Olympic Games of Helsinki in 1952.
His personal best performance in the pole vault was 4.30m in 1959 which was not a Greek record at that time.
Efstathiadis participated in veterans' games many times since his "hey day" winning medals well into his 60s!