the brightest i know is a light sold at int'l outdoor which hits 900+ lumens on a single 18650.
Other single 18650 notables are:
1. Xeno G42 - furthest throwing single 18650
2. SC600 - who hasnt heard about this light?
3. EC2 - Smallest 18650-based light
900 ANSI? not sure i believe that. its probably at the source, making it around 650ANSI, really nothing special.
AFAIK, they're all regulated lights. the klarus steps down from turbo to high after a few minutes, but its not becasue the current is lower, its because its programmed to do that. just stay away from LED LENSERs and maglites. some of them are not regulated.
Sunwayman t20cs is another of the brightest. but really, to your eye, the difference between 600 and 700 is very little. if i gave you one 700, you turn it on. gave it back, waited 5 minutes and tried a 600. you wouldn't know the difference...
more important to think about if yuo want throw or flood, useable spill, spotlight, battery life. much more important than getting that extra 20 lumens. a very significant proportion of people here don't use the turbo mode very often at all.