Building my first barebones and have that 4-pin P4 branches off of the 8-pin MB power supply. I keep going back to that as a nice, short alternative for my rear-of-case fan but panic about using juice intended for the MB.
I have a Gigabyte LMT78-USB3 with the single SYS FAN out going to the intake Zalman FB3 and the outflow fan (generic ThermalTake) is orphaned. I was thinking of leaving that steady at 5 volts as the ThermalTake Versa II case is more venting than solid panels, it seems and this is a home computer, no gaming and occasional music recording, home video editing.
I also have an FDD open as well as 4-inline pin Molex connectors. LSP-550 (Ultra/Tiger Direct power supply 550W). FDD is a match on connectors... :-) I see all these Molex 4-pins to fans (some offering 5V/12V options) but I do not need another foot of wire, I would prefer "species changers" (instead of calling it "gender changer"). Tight budget also calls for a simple solution instead of nice gear :-/