I find all headlights seem to be useless in fog and driving snow as well. The best solution is some dedicated fog lights mounted low, just below the bumper works fine, the bumper helps to block light reflecting off the fog as well. A good quality set of Hella's, Bosch or Cibie's(if you can still get them)work very well. Whichever brand you use they must have a wide and flat beam pattern, the idea is they illuminate the surface of the road only which can be seen a lot better than if your cars lights are lighting up the fog before the light gets to the roads surface. And yes, an added hid system to those fog lights will make a big difference, especially the brighter 3000K to 6000K types, although I must say I have not tried the weaker 8000K to 15000K, who knows, maybe the blue or purple light they produce might have some advantage although I think the yellow of the most powerful 3000K is the best choice. If you have daytime running lights, they will negate the effect of those foglights to a large degree, the more powerful the drl's the more reflection you will get off the fog. Foglights are best used with the running(park) lights on and the headlights off. You might want to check your local laws, they may demand that you have lights on that are at a certain height during nighttime hours.