9V will "overdrive" the KL4. SureFire do not recommend you do this because they have designed and tweeked the KL4 to work best on the E2e body powered by two SF123As.
I asked question, and PK responded. It uses a boost circuit, and as such is not suited for 3 123's. He said that the KL5 will use a different circuit. He did not elaborate on what type of circuit.