I have been running two different old style L1 heads (both ML1's, one UW0H, one SSC V0) on an E1E body with 3.7V RCR123 for a while now. I run it with a McGizmo McE2S two stage switch, so I use it on low 80% of the time. Hight for fun, not usually necessity. I have run it at most 15-20 seconds on high at a time. It has worked fine for me with no problems, but it is still a risk and YMMV.
I used it yesterday in a corn maze just north of Detroit, and I got lots of "nice light!" complements when I used it on LOW (22ohm McE2S SSC version, though my UW0H Lux3 Milky mod is also very bright) as it blew away everything else out there lighting up signs and maps in the maze with its wide flood optic. On high (est. just under 200L) it was too bright to look at anything up close as it would totally kill your night vision. I still had to be careful with low so as to not relect the beam back at me.
Running it conservatively on CR123 primary or 3.0V RCR, it is a decent long running light. I'd guess around 25-35L too. It's great for camping on 3V, so I have a very low low for in-tent use and high is still enough light for everything else and runs a loooooong time.
The old style L1 SSC head on E1E body and McE2S is one of my top 3 favorite lights. SSC'd Gladius and HDS EDC U60 are the other two.