toyo chick:
I have never heard of x-type HIDs. Are they true HIDs (come with ballast and ignitors?) or are they just halogens painted blue and labeled "HIDs"?
If you want a slight blue color, get the 6000k. That what I got. Right now they look pretty much pure white, but after 50-100 hours of use, HID bulbs color shift about ~250K. I wouldn't recommend anything over 6000K, there just isnt enough "useable" light for night driving and you might attract the attention of the cops...
PS-I posted this in another section, but here is an awesome faq about HIDs, basically everything you ever wanted to know and more.
http://faqlight.carpassion.info/hl-hid-bulbs.htm