Oooh, goody a post about colour and light.
OK, for those who dont know, degrees kelvin is a standard for measuring the colour (hue) of light ONLY, it has nothing to do with intensity (lumens), or power (watts).
The reason 8000k bulbs (and over) are dangerous is due to the fact that bluer light diffuses more readily than any other, causing glare and eye fatigue. This diffusion occurs in the atmosphere, and is far more pronounced in fog & rain, as you have just added millions of tiny prisms that will allow the light to diffuse further. Think of a rainbow, ever noticed how the bluer end is always thicker, or think about the reason we have a blue sky and why water appears blue.
5000k - 6000k bulbs are seen as being a comfortable alternative, because that is the hue of light the eye is most accustomed to, industry standards rate daylight (white light) at around 5500k (this varies throughout the course, and conditions of the day), the reason the manufacturers choose 4300k, is to do with both the natural (highest) output of a Xenon bulb (i.e without the colouring agents added), and the fact that while 5500k is considered daylight, tests have proven that when driving at night this colour temperature still causes a small amount of diffusion in rain and fog, as smokey mentioned before, yellow light has a lower amount of diffusion so it cuts through the rain & fog, rather than refracting.
The reason a 6000k bulb will appear to illuminate a road sign before a 4300k bulb, is due to the point I made earlier about diffusion, you will definitely see the highly reflective sign earlier with 6000k because your photons are spilling out and bouncing all over the place, however it will become legible a lot quicker with 4300k bulbs, as the reflected light will come back to your eyes in straighter lines. Which also highlights the reason we have headlight washers, they are there to prevent dust & dirt on the lens diffusing the light too much, causing glare.
It is also worth noting that a 55w ballast will throw a different colour of light than a 35 w ballast, from the same bulbs, and yes the projectors and lenses make a big difference in the output of light.
I run 3500k fogs, 6000k mains & 6000k 55w high beams.
And who else hates people who stick HID kits in reflector type housings ?, now thats dicing with death.
Nearly all men can stand adversity. But if you want to test a man's character - give him power.
Abraham Lincoln