Something else to keep in mind is that if you increase the intensity much above 5000-6000k, the light emitted actually becomes less usable by the human eye. Although the light may actually be more intense and brighter, the human eye can't process it as well as a lower number, so it will actually appear dimmer and slightly more blue/purple when you look at it.
I have a 35w 5000k low beam kit on my 07 WRX and it provides significantly more light than stock halogen bulbs and looks slightly more white than a 6000k + kit, so that's a nice option if you want your lights to be "slightly less illegal." My 5000k kit still looks very much not like the stock halogen bulbs and very "hid-ish" without being too obnoxious since I have the light beam set slightly higher than stock (stock cut off was entirely too close to the front of the car for my tastes, so I adjusted both lights up a tiny bit by turning the adjustment bolts behind the headlight housings a little bit with a wrench). I've had mine installed for over 30,000 miles and over 1.5 years and haven't gotten any negative attention from the law, although I live in MD and the police seem to be a little more lenient here than it sounds like they are in CA.