I’m finally going to throw something in my Solarforce L2R. It’s been sitting empty now for over a year, what’s my brightest option for a drop in to run off two
eneloops? Anything in XPG2 or XML2?
I would guess the XP-G2.
According to the spec sheets @ 350mA (with 5700K), the XP-G2 is 138 lumens. I’m sure the lower voltage ranges would do it well. I just don’t have experience with any XP-G2s to steer you in one direction or another. But it looks like we have XM-L-like efficiency in a smaller package with some better throw in the XP-G2.
Hey, lookie there…our registration dates are the exact same day!
Wow look at that and almost the same post count too! 
Thanks for the recontamination!
Ultimately brightness is determined by current to the LED and the LED’s efficiency. The issue is that most P60 drop-ins are not intended to run at the 2.4-2.6V range 2 NiMH AA batteries put out. But, there are a few out there that drive 1.2A to the LED from 2AA’s. If you’ve only got ~1.2A of current to play with you’d want the most efficient LED possible to maximize brightness.
If you are using 2 x AA and the driver suits, I love the XP-G2 at the lower current output.
If you dont want to use a 14500 Li-Ion with a dummy, you could try using 3x2/3 AA NiMhs. It would give you almost 4 volts. If your springs aren't long enough you may have to employ a small dummy. I use this set-up in a 2xAA mini-mag with an XP-G2, and its bright as hell. Each cell has a stated capacity of 700mah.
700mAh seems a bit low for the size of the cells. That’s more what I would expect from old NiCads.
FWIW, Customlites.com lists a 2AA XP-G2 P60 drop-in with 350 OTF lumen. I don’t know of anything brighter.
the solarforce 1-mode XP-G dropin is rated from 0.8-4.2V. I just measured mine at 980mA on a pair of slightly used energizer lithiums I had laying around - that’s pretty decent in my opinion. In fact, I bought two more of those dropins just for the drivers alone. Unsolder the emitter and replace it with an XP-G2 for instant satisfaction.
I quite like the 3 mode no blinky version of the low voltage XPG drop-in from SF. It’ll do a little over 1.5A on high (using a single IMR).