It sounds like you and I have about the same goal for HIDs. I have done a lot of talking with the guys at retro solutions, and they are way cool (as I am sure you know) and more than willing to help, plus they are reasonably priced and havent heard any complaints about them.
Anyway, from what I understand, the 4300k is the whitest, most usable light. For some compareson, it is the most common on the bmws, lexus, etc from the factory. The higher the temp, the more blue the light gets. The lower the temp, the yellower it is. You also lose lumens the more extreme you get in each temperature.
Also, I have been told that the digital ballasts are more reliable, as well as last longer than the non digitals. Between 35w digital and 55w digital, I guess there is a noticeable brightness change (55w being brighter).
Oh! And any option above applies to low beams, high beams and fogs.
This concludes (and encompasses) everything I know about HIDs LOL