SYDNEY, March 30 : Surfing's elite world tour kicks off this week at Australia's Bells Beach with Stephanie Gilmore, Carissa Moore and Gabriel Medina returning to the circuit to face off against a new guard that has raised the performance level in their absence. The trio, who stepped away for a variety of different reasons, might find a different level of competition on the 12-stop tour, now in its 50th year - particularly on legs that feature large, powerful waves.   "I am so stoked to be back,