I got the 6k in my suburban and 5k in my GTP for both foglights and headlights. I also put a set of 6ks in a ford edge for a frind both headlights and foglights. I know he loves them.
The 6ks have a slight blue, not alot but you can tell. The 8ks are really blue. The 5k are more white which goes good with a red car. The higher the number the less the light output. So 5k has more output then the 6k does.