Our bulbs are d2r. As far as the different kelvin ratings go I don't think it matters what level you put in. But 4300k apparently has the best light output. Basically the different ratings produce different colours if that makes sense. My lights give off a good beam at the moment but the haze that was on the lenses before had a really bad effect on the amount of light getting through. I can only imagine if I splashed out on new headlights the beam would be even better