"So, the 25% bonus to Legendary drops in Nephalem Rifts is multiplicative and will actually stack with the scaling Legendary drop rate bonus in Torment 1-6.
This means if you're playing through a Rift in Normal-Master, you'll have a 25% bonus to Legendary drops. If you're playing through a Rift in Torment 1, you'll have a 43% bonus to Legendary drops (1.15 * 1.25 = 1.43). If you're playing through a Rift in Torment 2, you'll have a 65% bonus to Legendary drops (1.32* 1.25 = 1.65). And so on. "
http://us.battle.net/d3/en/forum/topic/12413271220#2
"So, the 25% bonus to Legendary drops in Nephalem Rifts is multiplicative and will actually stack with the scaling Legendary drop rate bonus in Torment 1-6.
This means if you're playing through a Rift in Normal-Master, you'll have a 25% bonus to Legendary drops. If you're playing through a Rift in Torment 1, you'll have a 43% bonus to Legendary drops (1.15 * 1.25 = 1.43). If you're playing through a Rift in Torment 2, you'll have a 65% bonus to Legendary drops (1.32* 1.25 = 1.65). And so on. "
http://www.diablofans.com/forums/diablo-iii-general-forums/diablo-iii-general-discussion/84104-torment-slider-increased-legendary-drop-rates-for