Knowing that I was looking for a flicker I was able to discern it but only after setting the light down so it was not moving and removing any other light in the room so I could concentrate solely on it.
I wouldn't call what I saw a flicker. I could see what I would call a cyclic pulse in the intensity. This is something I had not noticed in working with this latest version of converter but in my defense it is not that obvious or blatant, at least in my perception.
I also realized that this might not be unique to just this particular light and it's not. I built a couple more XML-LE's and confirmed that they too display this behavior. I am confident now that this artifact in intensity is inherent in the nature of the converter and possibly the programing of its control chip.
I put one of the XM-L LE's in a Mule head and introduced it to my integrating sphere. I had the spectrometer software log the flux (lumens) with no averaging and scan sampling taken at 50 millisecond intervals. In graphing the flux on the y axis you can see basically a straight line and then a time segment where there is a flat sine wave repeating a number of times and then back to straight. In the sample tested, the low in the sine wave was about 178 lumens and the high around 185 lumens and the interval from low to high was around a third of a second to a half second in duration.
I suspect that this artifact in intensity variation is a result of the converter compensating for change in heat and Vf but I will need to pass this information on through to the designer of the converter in hopes of getting a more informed answer and hopefully something I can understand.
At any rate, I believe in all fairness and in the spirit of full disclosure I believe this quirk should be identified as a potential con as regards the buck/boost converter. In real use I would imagine this artifact would be viewed as a non issue for the most part but if the light is held steady and one concentrates on the beam and not what is being illuminated, it is apparent. I think my choice in words of calling it an artifact is appropriate here but that's just my opinion and perception.