Isnt there a 1xCR123 roundup or something in the sticky?
I would guess that since a CR123 has 3.0 volts (4.3 rechargable), that its only limitation would be heat output for such a small form. In other words, there isn't any fancy electronics needed to get the most out of the emitter. Most will be direct drive at about 1 amp.
The most efficient emitter is the XP-G R5 right now, so I'd bet that pretty much all the XP-G 1xCR123 lights are going to be pretty close in brightness.
There may be differences but I doubt you could tell that much of a difference.