k stands for kelvin. kelvin is a system of measuring heat, like degrees or centegrade. when they say 8000K, they're talking about a heat range of up to 8,000 kelvin, or at least that's what i've heard. i could be wrong though.
i personally have hella headlight bulbs (low beams) and silverstar fogs.
the title of your thread mentioned volts and watts. all the factory bulbs run on 12v. the headlights are 55w from the factory, the fogs are 42 or 43 watts or some oddball number like that. i've got 65w headlight bulbs and 55w (maybe they're 65w) foglight bulbs installed currently. they're plenty-bright for me.
the fogs seem to be brighter than the headlights, but i beleive that's because the reflectors were never designed to accomodate such a bright bulb.
as far as something to match HIDs, i'd look in the big headlight thread. i think its a sticky actually.