3000k is yellowish, 5000k is blue, and the higher the kelvin number after 5000, the hids will not be as bright. So a 6k or 8k is not brighter. The hids will not perform well in the stock headlight housing, as it isn't designed for hids. That is why a projector/retro-fit kit was recommended above. The light will be brighter, but the shape of the housing will scatter the beam.
You will also have trouble switching the high beam on and off repeatedly, as it takes the hid ballast a moment to ignite the bulb.
If you want more light to see clearer or further with, add fog lights and/or get a projector/retro-fit kit for the hids.