Romisen lights 3-6V? 8.4V?

I have a lot of Romisen lights and have one or more copies of almost every model. Most of the Romisen lights are officially rated at 3-6V suggesting that one could use 1X4.2V RCR or 2X3.0V primaries. I just got a new batch of RC-M4 lights and noted that the emitter in the P60 module seems to be a square CREE with four copper wires on a silver background. FYI, I'm running two of these on 2X16340 TrustFire cells (8.4V) without any short-term problems. Seems brighter at higher voltage, so I'll do some tests with a light meter later.