You can only use LuxIII's with the NexGens. The NexGen 750 will be brighter with less runtime. If you plan to use it in constant on for long periods, I would recommend less power. The only reason I could think of wanting the higher power for long periods of use is that you need to illuminate targets more distant. If this is the case, go up in reflector diameter and down in current; I.E. an Aleph 1 with a NexGen 500. Now if you want the high level in intermittant use and will be using the low for long runs, the NG750 is a good choice on the Aleph2. I prefer the higher powers for high but I don't use the lights in high for long durations. A small light like this is not typically a "walk about" light. /ubbthreads/images/graemlins/icon3.gif JMHO and you need to decide what your needs as well as wants are! /ubbthreads/images/graemlins/tongue.gif