My Trinidad Moruga "Scorpion" peppers top out at 1.8 Million SHUs ...
... as tested by the food science boffins at US Davis. In theory, they can go over 2 million SHUs, I suspect I'm babying them too much. Peppers need stress to develop maximum heat. I believe the Carolina Reaper can go up to 2.2 million SHUs in the right conditions, I haven't tried growing them yet.