I have a G2 but have not run the RCR's. RCR's normally come off hotter (you said 3.7V) than 3V, but you said you had a range up to 9V, so you are still under the 9V and should be Ok. I just recently put an after market Cree R2 LED ($19.99) rated at about 230 lumen's in my G2. Works great, and gives longer run times for my 2XCR123. Here is the link. Look down to the Cree up-grade.
http://www.lighthound.com/
BTW, the Cree has a voltage range of 3.6V-12.6V.