I went with the 5k 35w. However I think they sent me a 4300k & 5000k headlight bulb...they look different colors now. Been running for almost 5k miles.
My ONLY comment on the DDM HID's: If you plan to run a CB or HAM radio, you WILL have interference. Their slim ballast's are NOT shielded.
Other than that, they are great for the price.