Great that you have a LW4000 as this can be used for comparison. Since your quest is to purchase another light, what specifically are you looking for that the LW4000 does not give you.? You mentioned "bright" several times, and I gather you want something brighter than the LW4000. The Arc-LS may fit this bill and it will be a lot smaller than the LW4000. This biggest issue would be run time (4+ hours) and the "123" battery changes. But, it's a dam bright light in a small package. Anything brighter that this may not be provided by an LED source. Maybe if you specify "bright" using examples, we can better help you out.
As for trying to unscrew that top of the LW4000, the only solution I have is "elbow grease". You might want to wrap some sort of rubber around both sections and try again. Remember to not torque it down so tight next time. Also, make sure the turn is clockwise to each other!