as far as i know 4000k is brightest and legal thereafter its not i had and would recommend 6000k as best mix of white/blue, 8000k is very blue and higher starts heading pink i havent fitted them to my skyline but i bought an after market kit which was model specific h1 i think it was, as far as heat goes didnt have any issues with this, its a fairly straight forward upgrade just mount ballasts hook up and away u go
important to note it is illegal if you dont have washers and/or auto leveling for headlights..