The light output is better and it's in a projector so you won't be blinding people either, I say do it. Only issue is that to get to the fog bulbs in a GXP you either have to take the entire plastic splash shield out under the car or remove the plastic grille piece. I've always done the latter but you always take the risk of breaking the plastic tabs holding the grille in place.
That's the best pic I have of the HID fogs. I was working on a projector retrofit with my headlights and was comparing the 4300K fogs with the 5000K headlights.