regardless the size of the bulb...

Which of the 2 shall i choose...

The S400DD - 5200K...

or Pulse Strike T15 - 4000K

the 5200 seems whiter.. (if i remember my electronic class...)

but i other than that... which one is best?

Pluse Strike is brighter, S400DD is whiter, which is more important to you?

Its an excellent question...

Considering that my projector will be at least 12 feet from screen... which one would you suggest? a brighter... or whiter?

I know its all in the question... but i need experieced recommendations.. :-)

Its really a personal preference thing, both will work, the distance doesn't really effect the decision. The S400DD recently changed length and seems hard to get so I suggest the Pulse Strike until Ushio gets things sorted out. Brighter is better and you can adjust your LCD controls to make up some for the color.