I've been using a E2e / KL1 with the CR123 Dspeck extender so I can use 2AA... Should get between 2 1/2 - 3 hours runtime (far short of your goal).
With an additonal AA Dspeck extension it should get around 5 hours? on 3 AA.
The UBH would look way 'cleaner' but I worked with the components that I had and that I could get at an affordable price... if you have an E2e Kl1 already it might be an option to explore.
Or, if you have a KL1 head, maybe the TW3 will work with 2AA? That would look a lot cleaner than the E2e body and an extension -- but would not have a TS.
Of course if you don't have a KL1 already, it's not the best 1W out there, from that I have seen/heard they tend to be really off greenish color.
editied to add --
I really like the idea of a Mclux head of some sort, it seems that would afford a lot of choices in sandwich/led combinations and be very upgradable. It could go on a UBH or an E2e w/a extension. Downside is that the Mclux heads and innards would be $$