5000k is a pure white. just BARELY any blue noticeable.
6000k is much more blue. Kind of like the tuner halogen bulbs with blue glass... Mostly white, but a lot more blue. Oncoming traffic will see them mostly as blue.
6000k is cool if that's what you want. Anything over 6000k really has horrible output. I personally would never go over 5000k cause I love the pure white look. And it get's the most light on the road.
I haven't ordered yet. Want to soon.