RE: How to convert an ATX power supply to rc use
If your charger will function satisfactorily at that voltage, I wouldn't drop the resistance any further. The marginal voltage gains are usually small with an associated increase in PSU load. As a quick test, temporarily wire the second resistor in parallel to the first. This will give a 5 ohm load and you can meter to see if you get much in the way of a voltage increase.
andrew