I think sometimes it depends on the brand- like clothing, not all large shirts are the same size. But for the most part , I believe the whitest color temperature is gonna be in the 4300- 4500 kelvin range. BTW, Chip, your eyes ARE going bad, lol
http://www.mediacollege.com/lighting/colour/colour-temperature.html
I don't know. I've got 4100K Silverstar Ultras in my HIs and lows. I know they're supposed to be the purest white you can get, but I still think they look yellowish and somewhat "dirty". The 6000Ks are brilliant!