In reply to All:
Many, many thanks for so many useful contributions!
I'm now mulling over various different options:
1. The actual Gamma that lithos offered for sale (I appreciate the offer, thank you, I'm seriously considering it)
2. The Kathmandu Gamma clone - unlikely as it doesn't have red light and appears to be out of stock
3. The Petzl Tikka XP2 - I still have my doubts about stability but various people's recommendations are beginning to sway me
4. The Lifesystems Intensity 80 - I discovered this by searching for Gamma on outdoorsmagic.com and it seems to be a Gamma clone from the same factory with the addition of a motion-controlled switch that you wave your hand at to turn it off or on. It sounds nifty but I'm wary of it being a potential source of malfunctions or irritation when moving my hands past my face to climb.
5. Climbing Technology Lumex Pro - Yet another Gamma clone with a more powerful main LED and adjustable lens. It's tempting but it no longer seems to be available at the only shop I could previously find it at (which is very frustrating because I was leaning towards this option and it still appeared to be available as recently as yesterday!)
I'm sure you're not too interested in my obsessive list-making but I thought I'd pop my thoughts up here in case anyone else has a similar dilemma in the future and wonders what I concluded.
(Option 6. Taking The Lemming's suggestion to the obvious 18,000 lumen extreme: )