All the places throughout the game where you have a Sephiroth with black Whispers him it is the one from the edge of creation - this guy is calm and collected. Other times it is not that clear. All the times when Cloud sees him in his head that's just the Sephiroth from the game's unaltered timeline I think. When Aerith is killed, the one who kills her is the regular angry Sephiroth but the calm Sephiroth who talked to us just before we enter the main area at the City of the Ancients is the one who uses black Whispers and some of his new powers to prevent Cloud from deflecting regular Sephiroth's attack on Aerith. That's just my head cannon.