Just did some 6k's in my skyline last week, and some in my brothers Mazda SP 3, look great, very nice. 5k is about white, 6k gives the smallest bitta blue, but still gives the perfect clarity and vision. And generally seems not to get too many people pissed off at ya. I had more people get annoyed with my fog lights on, on my Pulsar than they have with the HID's on my Skyline.
I'd not recommend above 6k. Only go for 5k or 6k lights.
I got mine from http://www.point-blank.com.au/ (via ebay - links on their page any way). Great Phillips globes in these kits, and come in EVERY type at EVERY different colour temp.