The Kelvin colour temperature chart is pretty static... yes some bulb manufactures are slightly different in colour, brightness, and look... but 3000k will always be yellow and 12k will always be ricey purple.

And 8000k+ on a non projector setup may get you pulled over for looking too bluish purple (it screams I am not stock and am after market, which will then leaving you pulling magic tricks when the cop asks you to show him your high beams... which no longer exist by the way in most generic HID setups).
There are dual bulbs now (half halogen and half xenon) which will still allow your high beams to work. The only true high/low beam combos only exist in a projector type setup (H4 I believe).
I would also recommend going with a very good brand... HID bulbs are not cheap to replace (about $200 CDN for a pair).
I would highly recommend Phillips... if you can't afford that then go one step down to McCulloch... then go cheaper then that at your own risk (mind you, you can also go more expensive then Phillips if you wish).
Do your research until you fully understand what you want... get what will provide the most light without annoying other drivers, last without needing constant bulb replacements or ballast, and get what will not get you pulled over.
Also look into a wiring harness to protect your car's stock wiring.
gl
p.s. I did not put any time into researching anything I wrote... just writing off memory when i did the research myself way back... so my apologies if any of the info i have stated is slightly off.