I don’t use CR123A myself, but I checked HKJ’s review of a Panasonic one:
and a single CR123A won’t do 100lm for 5 hours - it just doesn’t have the capacity. 3.5 to 4 hours would be more like it. Of course, you could carry an extra cell or two, which would also protect you from the risk that the light might be accidentally turned on while it was in your backpack.
For this specification, I would be using an 18650 cell, which would meet the runtime requirement with ease. It also has the advantage of being rechargeable. Unfortunately, the light would obviously be 50% longer.
A 2×AA light with lithium primary AAs (1.5V, about 2500mAh) in it would also just about meet your runtime requirement, at the price of being longer still.
If 18650s were acceptable, some 18650 lights are compatible with 2×CR123A, if that’s important. Someone else would need to recommend lights like that, though, because I have no experience of them.