5400K make quite a difference in color and visibility. Anything higher than that, it seems to hurt a bit in visibility, but you get bluer and almost purple.

from 4300K to 5400K/6000K = visibility better;
> 6000K = visibility seems worse.

The car with 8000K was not my car. It was a friends vehicle. Also, I am not sure which bulb manufacturer he was using. He had stock ballasts.

I think staying with 5400K or 6000K you will see a good difference.