Are there any bulbs that would fit this and run comfortably off 3xCR123?
There are plenty of 6V 10W G4 base halogens allegedly available in 1.66A that you can test overdriving on 3x CR123A. Something like
Osram 64410 perhaps, or
Philips 6605 maybe, or
Osram 64423 possibly. There are also 6V 5W G4 base halogens ostensibly available in 0.83A that you can test overdriving, like
Higuchi JC5603, God willing. My understanding thus far is that overdriving bulbs will cause them to draw more amps, so be aware of that.
Disclaimer: I have no idea if any or all of those lamps suck for flashlighting.
Also, taking votes on 2x17500 vs 2x16650 with extender on my M3T.
If you're asking about lamps,
Tad's A7212 7.2V 1.2A bipin is nice if you have his M3 socket but idk a source for his lamps anymore (bah, that won't work in M3T, srry). But Mark's
HO-M3T 380Lm 1.81A-2A lamp assembly is available, as well as his
IMR-M3T 700Lm 3.03A-3.4A lamp assembly. Actually, he recently told me he doesn't keep any lamp assemblies stocked. He builds them to order.