I have a Fenix BC21R (version 1 with the beam cut-off optics) that I slipped a Panasonic 3600 mAh 18650 battery in (it came with a 2600 mAh). That bad boy will flash all day.
In my BC30 V2.0, I'm running a pair of their (nominally) 3500 mAh 18650s.
I'm glad that Fenix continues to have a presence in this market. IMHO, they are getting a lot of stuff right on these.