Maximum recommended continuous discharge rate for LiCo cells (that's protected li-ion in most cases) is 2C or 30 minutes, which for RCR123s means 1.2A give or take. The P91 draws ~2.65A on li-ion cells. At the load of a P91, most RCR123 size LiCo cells will just fall on their face. You might get 10-20 cycles out of them at 5 minutes per run before they would either explode or you would have to retire them.
Most Protected RCR123s will not even light up a P91 period, some will on multiple tapping of the tailcap to trick the PCB, this is not recommended as it's hard on the PCB and obviously means the cell is being used in a configuration that is beyond it's ideal maximum safe limit.
Always read manufacture recommended guidelines for usage on lithium-ion cells. If your source for RCR123s does not have any information available to you about the cells, I suggest not purchasing them from anymore. The power consumption of many of these lamps can be found in a sticky in the threads of interest... Or you can see most of the safe li-ion powered incandescent configurations in the "li-ion incan guide/chart" linked in my sig line
As Outdoors Fanatic said, you CAN use AWs new IMR16340 cells to do this configuration and it will be perfectly safe. Runtime would be around 10 minutes.
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Oh.... you mentioned you wanted throw.. The P91 is a pure wall of floodlight, it's the last bulb you should consider if you want throw.
Try an HO-9 from LF on a pair of IMR16340s, it's not a bad combo. Ideally speaking, consider a KT2 kit to go with a pair of IMR16340s.