Going upwards from 4100K means that your lights turn blue at the expense of total brightness and yellow colour. theoretically if the same brightness were to be kept you would have to increase the wattage of the bulb from 35 to 40W and redesign the ballast. This would be costly and probably not pratical int he automotive world and that is why much of the automotive hid are 35W.

Of course you could always say the 5000,6000,8000 etc bulbs look cooler. But nothing is really better than a 4100K. Dont believe the hype.