I know about the 5v and 7v mod but it's a bit too low for the fan to work in an optimum level. I understand that we can get it running at 9v but probably need to place a resistor in the "red wire" from the PSU to fan. If so, what is the resistance (ohm) I should put?

I don't need a fanbus or controller but having it running at 9V-10V is simply fine. Anyone can help? Also, If I mod and plug towards the motherboard, will the fan run at a lower voltage?