Torment VI is no longer the hardest setting in Diablo III. With Greater Rifts -- tiered dungeons -- added, everything beyond Rank 25 is harder. So completing a Rank 40 Greater Rift is quite difficult. Yet, some folks can complete them in under eight minutes.
You have 15 minutes to do the run, every mob has billions of HP and if you don't stun them in time, they can basically kill you in one hit. Still, Diablo III veteran Alkaizer (he was the one reaching Paragon Level 100 first in the world) and his buddy Philos were able to rush through Rank 40 with plenty of time left. And they did it with Season 1 characters, which means these characters didn't even exist two weeks ago.
Here's the VOD of Alkaizer's stream below, but more importantly, click here for the part where all the madness starts when they enter a Rank 40 Greater Rift. They're lucky with pylons, mob types and mob density but that doesn't make their run less impressive.
Alkaizer's Stream [Twitch]