"I always thought he'd be Vader after the whole...
Mace confrontation and the Jedi Temple raid. "
According to spoilers, this is when Palpatine finally spills the beans about himself being a Sith. Then he shows off his awesome abilities by killing Mace. Therefore, Anakin would become Vader after this scene, but before the suit (which was only intended to keep him alive, not to make him a Sith.)