For single cell as it is now, the 17mm driver is perfect - lots of options, but of course I only want a FET+1 anyway. But yes, for 2-3 cell options, the bigger driver is almost a definite.
Ohh btw - Simon gave me 15% off the entire order 
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Wish I could jury rig an e-switch in this light though - would be perfect for my new 45/85 e-switch firmware (in here: https://budgetlightforum.com/t/-/34900). I always preferred e-switch's, but now, it's a whole new realm with almost all the bells and whistles, and room to add even more features. Just give me a side mounted switch with 2 wires hanging off of it in the pill, and I'll be happy.