Headlights?!

I bought new Xenon Super White HID bulbs from Circuit City. I was assuming that they were going to bve brighter than my stock bulbs but they seem pretty much the same in all that. Then I went onot eBay and looked at the bulbs. It says in the manual I need 9007 bulbs. Then from there they are different ones online. Some with different K's they start from 4000K and range all the way up to 8500K. Whats the different in the K's and can my 2003 Cavalier use any K value or only to a certain level and what does the levels mean?

k= degrees kelvin. higher is whiter not brighter.

If you want brighter spend the money and get real hid headlights