I have seen the Gemini, the light output is on the dim side (7 hrs runtime on 3AA). For Sure Fire beam quality headlamp, I use PT Vortex with KPR103 and NiMH. It is even brighter than an E2 but with AA cells. Yes, this is waterproof.
I have the Streamlight Trident (the one I have doesn't have Streamlight brand but from the same manufacturer). This is a very good LED headlamp but the beam from the Krypton is pretty bad and very yellow. I replaced the Krypton with another LED and make it an all LED headlamp. I used this light a lot until lately, I replaced it with a Zipka-like light.
This Zipka-like light is exactly the same as Zipka (it seems produce from the same injection mold and I suspect it comes from the same manufacturer) with additional functions. It has a magnet on the trap that you could stick it on your car or any metal stuffs. It also has blinker function and make it a good roadside emergency light (more than a headlamp).
This LED light (strapped on my wrist like a watch) is good combination with PT Vortec on my head (for hight output) during camping or night hiking.
Alan