i've been thru many many many different kits over the years. The less the "k" the higher the output 3000k (yellow) the brightest, 4000-6000k or so is gonna give ya close to white, 8000k usually give pretty dark blue, 10000k is a lighter blue (more blue-ish white), and 12k and higher is towards the purple side of the color range (12k and higher has the least light output of HID's but still WAY more than any type of factory bulb). I have off-brand 30k in my wifes s10 and silverstar bulbs for her brights and they are similar output range.
My favorite for all of them is 10k. Works the best in the rain/snow/clear weather and doesn't have enuff color for any type of hassle by the local police.
Here is a pic of my old charger with McCulloch 10k, and i took those out of my charger and put em in my challenger that i have now and i love them. if i ever buy any more 10k i will probably buy ballasts from DDM tuning, and buy replacement 10k McCulloch bulbs from Xenonking.com (kits from xenonking are around $300 compared to replacement bulbs run around $100) In my last couple show cars i ran DDM tunings 12k, and those are a light purple color and look killer too. Its more of less of personal choice if your going for light output or if you want something that makes your truck look cool coming at you down the road. if your looking for color i'd go with 10-12k(unless you want a LOT of blue, then go with DDM 8k). If your going for light output i'd go with 6000k personally (but then again its all personal preference, i'm just here for guidance, lol) Hope this helps, any questions lemme know!
heres a couple pics of my charger with McCulloch 10k
stock compared to expensive 10k
heres DDM 12k on my envoy (idk why but my phone makes them look a little more blue then they actually are, they are slightly purple)
heres McCulloch 12k that i have in my wifes dakota (wanted something dark purple to match the paint)