the 4300K HIDs are not yeloowish by any stretch, they are rather whitish... they are the factory Kelvin temperature used in the BMWs... they also produce maximum LUMENS among the HID kits sold out there... once you start shifting the color tempoerature of your light output, your will shift the light towards the UV part of the spectrum, thus the bluish/purpulish tint of the light, and at the same you will DECREASE the light output in lumens... The Lumens are what is illuminating your road in front of you.

I will not recommend going above 6000K, and if you wish to entertain the 10000 K lights, i'd suggest using them in non-vital lights, such is front fog lights...

speaking of the spread pattern, if you had the halogen, i would suspect you had "free-form" light housing, and placing a different geometry light bulb in that housing will give exactly the result that you have now...

on the other hand, if you have the projector headlights, also known in BMW world as ellipsoids, placing an HID light bulb in the ellipsoid designed for halogen bulb (my E34 had this set up) may throw off the light pattern, but not by much... even though the focal point is different, the mere fact of the magnifying lens will concentrate the light beam albeit it will be focused at a different distance than the original halogen was...

if you have a free-form headlight housing, i would suggest replacing the entire assembly in favour of the HID assembly, either OE or quality aftermarket... You will also need to reprogram the LCM to either acknowledge the new HID lights, or to ignore the error that they will produce on the halogen equipped car... for the programming, you will need to "change" the car's production order - it is doable with the NCS Expert...