i tried once,in my friend's cateye halogen 4aa light, with a pm6 xenon bulb powered by 4 energiser cells and its significantly brighter than the stock 2.4w micro halogen bulb. its still tad behind that of a pm6 on 2 cr123 visibly and with sanyo 2500s, the output is dimmer compared with the energisers.
i think this is a nice way to get a pelican reflector and at the same time upgrade the existing cateye 4aas if u happen to own one.(pelican reflector do needs some machining work for it to focus properly)