If you want functionality over looks, don't even bother with a 8000k kit. It'll output a very blue light that's way down on lumen count, when compared to the 6000k kit. Don't forget, the higher the colour temperature, the less light output the bulb will give.
My 6000k kit gives a pure white light output, even though it should have a slight blue tinge at that colour temp. That's probably because the colour temp of HID bulbs, normally has a tolerance of +- 500k. I suspect mine are closer to 5500k.
The actual light output from the kit I have fitted is also very high. I had 90w halogen/xenon bulbs fitted prior to the HID kit and the output now is easily twice as bright as it was, probably brighter.
Have a search round the web as, there are plenty of stores that will show you the difference between the various colour temps.
Also, if you find you don't like a specific colour temp, you can always change the bulbs to another one.
Paul