You can get a basic idea of runtime by dividing the draw into the capacity of the battery, but remember that some cells take a dive as you push the draw on them up.
For instance, even with 9500mAh cells, you won't get 2.5-3 hours from the ROP high. If they are good cells, you will get no more than 2.2 hours before significant dimming, and probably less. (I recall that the ROP high draws about 4.4 amps, divided into the 9.5 Amp hours of the cells and that equals 2.2 hours.)
The calculation though, is dependant on cells that will actually produce what they are rated at, and many of us know that only a few manufacturers of NiMH cells deliver the goods most of the time. The same for LiIon cells, where LG cells seem to be the cream of the crop in unprotected cells and Pila holds the boat for protected cells with AW producing a good product too.
If I were to choose, I'd run the ROP high (4.4A), then the ROP low(2.2A if I remember right), then the Reflectalite GH24 (1.7) for the best spread using the same voltage.
Bill