Oh boy....
Let me shed some light on this (pun intended):
OEM HID bulbs (Philips or Osram) are rated at 4100K. They have been this way since they were first released in the late 90's.
Here's the white papers for the Philips 85122 (regular everyday D2S):
http://www.nuconverter.de/assets/pbd2s.pdf
There are no OEM bulbs that are anything other than 4100K. Period.
Philips, Osram and GE do make some bulbs that are outside of this realm but, these bulbs are not sold as OEM and will not be installed from the factory.
The Philips Ultinon bulb (rated at 5800K) is the best known for it's extremely blue/white color temp. The unfortunate part is that the Ultinon bulb is about 800 lumen less in light output than the OEM 85122 bulb:
Ultinon white papers:
http://www.autolamps-online.com/gasd.../GE%20D26K.JPG
Osram makes a 5400K bulb but, it's only made in D1S form (B6 cars use the D1S bulb). Eitherway, it's still lower ouput than the 85122.
Honestly, the brightest bulb that you can possibly buy on the market today is the Philips 85122+. The 85122+ is a 4200K bulb that produces 3400lm of light per bulb.
Here's the spec sheet:
http://www.autolamps-online.com/gasd...es/d2%20PH.JPG
Also, all DOT HID systems are 35W. This means that you can't just slap a 50W bulb in them. You would need a 50W ballast to run a 50W bulb. Valeo does not make a 50W ballast. Hella does, Denso does and I believe GE does. Any others are aftermarket 35W ballasts that have been tweaked to run higher and will burn out sooner due to overload. You can't bump the wattage and not cause other problems in the ballast.
In a nutshell, any time you take an HID bulb and increase it's xenon gas ratio, you effectively increase the color temp. You also DECREASE the acutal light output. For a reason that I'm not completely clear on, the OEM manufacturers have not been able to get more than 3200-3400lm from an HID bulb if the color temp is beyond 4100-4200K. It apparently has to do with the properties of xenon gas and how it reacts to voltage.
The bulbs also contain salt crystals that allows the gas to support the arc of light. These salts and the gasses age over time and the bulb's color temp will shift higher than when it was new. As this shift occurs the bulb looks more blue/white.
This was extremely common on early 2000 cars that were fitted with HID hardware (Mercs, BMWs) and most are extremely purple now if they have not burned out yet. The key to this is that these purple lights are not providing good light on the road surface. You are dealing with a bulb that is near the end of it's life span and will not work for much longer.
If you take a look at the spec sheets I posted above, you'll notice a spec for each bulb called "Maintenance at 1500hr". This spec means that at 1500hrs of use, your bulb will only make 75% of the original light output (ie. 75% of 3200lm = 2400lm). This is the output of the Ultinon bulb!!!!
So in conclusion, you will always get the best possible brightness from the OEM bulbs. The 6000K and higher bulbs are not doing much for you and since you all are S4 owners and have HID hardware from the factory, you are effectively DECREASING the output of your lighting system by installing these aftermarket 6000K+ bulbs.
The choice is yours.
You can get with this \/\/

or you can get with that^^
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