Survey says, it’s the emitter.
I pulled the brass post on the driver, put a solder blob on it and checked it. Marginal gain. So I wired the emitter, in the light, direct drive to the 35A cell. 4.99A. There’s just not much there to be gained if I was getting 4.83A to 4.86A from the driver. This is top end, pure and simple.
So, I pulled an old XM-L2 off an Aluminum star and put it on a SinkPad, put that in this light and put the brass button back on the driver. Bingo! 5.52A in the light. Same driver, same cell, different emitter.
Edit: Oh yeah, the funny thing. The older emitter pulls 5.52A but only makes 1383.45 lumens. So, we were getting top lumens with lower current draw… higher efficiency all along. Funny, huh? We get all caught up chasing the current when the output is right there in front of us all along.
EditII: I did check direct drive with the Star in the light, it hit 6.11A but wasn’t being pressed down against the emitter shelf with no reflector in place, it started to get hot. But that tells me the driver in sheer top end with this old emitter is costing some half an amp, might be in the 22ga wires on the driver or just running through the circuitry, don’t know. (test leads I used were 20 ga. but about 4” long each.) Still, it’s fully capable of making the power given an emitter that will take it. Maybe I’ll check it powering a triple or the SBT-70…