I have 6000K TechOne kit from Protephile here on the forums.
I almost went with 7000K, then did some research about max light output and so forth. Turns out that past approximately 6000K, the light output starts to decrease, going down as your K's get higher .. not to mention that if your headlights get TOO blue/purple, you start attracting attention from cops.
I'm very, very happy with both the light output and the color of mine. Bright as hell and an awesome 'diamond' hue -- you can see both blue and purple, depending on the angle.