Riviera: For general, everyday driving for most people, I think 55w is way overkill. Any kind of city driving, it's just not necessary. 35w low-beam HID's are still a hell of a lot brighter then any halogen lamp, and combine that with city lights and you just don't need more. I do a lot of dark, backwoods highway driving, so I like a LOT of light when I want it, but honestly I think in 95% of people's lives it'd be ridiculous.
I have 35w in my lows with the retro, but I think I could run the 55w bulbs in those. It's so focused I think I could keep from blinding people with the right adjustment. The fogs I don't drive with anytime there is traffic because it just throws light freakin' everywhere. You can actually make out the radius of the light from the reflector, and it shines up a good 25-30 feet...street lights turn off as I drive down the road because they think it's daytime again....lol.
So...the short version is if you have good projectors, you could probably get away with the 55w bulbs with good adjustment on your headlights, but 35w are still brighter then a halogen light and in most cases would be plenty. I wouldn't recommend 55w for fogs if you drive around with them on all the time or ever in traffic. I guarantee you will make enemies quickly.
After taxes this year, I may get a cheap 55w kit to put in my retro just to see how it handles it.
Hope that answered your question.