Yes of course, I forget that this is an international forum. MOT is UK only in fact.
For a more useful reply:-
Useable light output for a HID bulb peaks at around 4300K for the same wattage input (they are all the same wattage). As you progress up the colour temp range, light output drops and the colour of the light changes. Beyond 5000K, they become increasingly blue looking and by 8000K will be purple looking. And by 8000K the useable light output will be noticeably lower.
4300K sounds a bit "yellow" but I have now found that most BMW's use 4300K as do GM in the UK at least. It looks white enough and gives excellent light output. Some BMW's apparently use 5000K as do some Mercs I hear.
So my advice would be: The very best light output, stick with 4300K. if you want a whiter look, go for 5000K for a minimal output reduction.
I have used 6000K on a old car with HID conversions and they were very good - they were so white that they did not illuminate the asphalt - white on black is black. They illuminated everything else well. The 4300K in my F10 illuminate everything and look plenty white enough from the driving seat. My wifes GM has 4300K and I would say that these too are better than the 6000K I had in my old car.