I've been using the Ultra exclusively with RCR123s for over three months, so I guess it's time for a run time test.
For the test, I'm using freshly charged AW RCR123s.
First....temperature. I held onto the body of the light for the entire test, and it never got beyond warm. I was able to comfortably hold onto the head also.
The head reached 112 degrees after 15 minutes, and remained at that temp for the remainder of the test.
I didn't measure the lux during the test, but it didn't dim appreciably.
The light shut off after 49 minutes.
While a sample size of 1 is far from conclusive, I'm now comfortable running mine on RCRs for as long as the cells last.
After about 15 minutes of recovery, one cell measured 3.208 volts and the other one measured 3.260 volts, at rest without load.
Grizz