I keep it at 6500K when I'm awake because for my computer, this is identical to not having f.lux open. I also have a properly-calibrated color profile in use as well because my monitor's color is notorious for being bad (the Samsung 2253BW). It's good for gaming, but bad for color - until using a properly-calibrated color profile!
Anyway, when I think I'll be going to sleep in an hour or two or three, I go 100% red. So to start with (or sometimes I do this last), I make a quick change to the Registry to set f.lux to 800K. When I do this, I also reduce my monitor's backlight brightness to about 0-10%, I set its color output to be 0% Blue and 0% Green with 50% red (the normal is 50/50/50). In addition, I go into the NVIDIA Control Panel and I set Digital Vibrance back to 50% because I keep it at 55-75% all day, depending on my mood or what I'm doing.
So in other words, when I want to unwind, I go red. :) The difference in the way I feel is actually pretty big. I really do begin feeling more relaxed.
As the time draws near to when I wan to turn the lights off and go to sleep, I turn off one of the two red LED lights in order to lower the brightness level. I have one floor lamp next to me, and another next to my bed which is about 9-10 feet away from me. So, I turn off the lamp that's right next to me at my computer. When I do this, I once again feel a difference; I begin feeling even more relaxed.
When I wake up, I swap the lights back to my normal LED lights and I'm good to go for the day. Of course, I also let in as much daylight as I possibly can, unless the sun starts making it too warm in here. :)
So yeah, I'd say that I have it nailed down, almost like a science.