The 9006 is a regular US spec bulb. The 9012 is HIR (High Infrared Reflective). The difference is that with the same wattage and very little difference in heat, you get a brighter illumination. The bulb life is about the same as well, unlike most over-wattage units of the standard design. There's no color antics either - no silly 'blue', just full spectrum and thus very truly white light. You need to trim the tabs to make the 9012s fit the 9006 socket, but it really is very easy. This thread details much of this, with links:
http://www.subaruoutback.org/forums/80-electrical-electronics/10077-bulb-information.html
Your fog (driving) lights are meant to be low and wide pattern, fairly close coverage. This is best for seeing the road lines when conditions are obscured, and for seeing potential hazards approaching from the sides - as in animals, like deer, elk, caribou, moose, etc. That's one reason I like to run my fogs when possible.