This is a subject in which I disagree with Pteam.  
Don't go over 6k.  Keep it legal.  The lower/whiter temps/colors have more throw and spill.  Anything between 4300 & 6000 will 
look like Litronics, as that is the range of your higher end cars (manufacturers produce street legal vehicles -they 
do not come 
close to 8-10k).  A lot of people think the higher the number the better.  That is not true when relating useable/visible light.
Also, the following image is fake.
 
 
This is the same image with saturation & hue levels adjusted.
And if any one wants to debate what I have posted, feel free to do so.  But please first research it in a capacity relating to 
Optics -not from eBay and sites that sell xenon kits or observations of seeing cars on the road.