Just to clear up a common misconception here, the 6300K/4300K/(X)K number refers to color temperature, which is the temperature an ideal black-body radiator would need to be to glow that color. It'll tell you how hot the filament in an average tungsten bulb will get (since tungsten generates light via heat and in most bulbs it is nearly an ideal blackbody radiator), but it won't tell you much about an HID's physical temperature, just its color. (HIDs operate via an arc, which isn't a blackbody radiator at all).

A good measure of how much heat a bulb will put out is its wattage draw from your electrical system, since this tells you how much total energy the bulb has to convert to light or heat, and all bulbs generate mostly heat. As HIDs are more efficient (put out more light vs. heat for wattage put in), they generally draw less power than stock filament bulbs and thus put out less heat.

So in short, don't worry about the heat from HIDs, especially when choosing a color.