I'll put it as straight as possible, don't skimp on HID kits. I bought mine thru a vendor on another Cobalt site for $130 shipped for one set, bought 2 and from the time I sent the money to the time I got them didn't even make it 24 hours.
One of my fogs burnt out after about 3 months of use, the ballast went with it, strange but crap happens, so with the money I didn't skimp on mine included a warranty and it was replaced no questions asked.
And 9007 is your bulb size, I have the 1st gen projectors which you have to mod to fit the HIDs for the return and there H1 and the fogs are H11.
I'm no expert but I do read a lot and I have worked on $million+ pieces of equipment at a theme park along with there electronics and now work at a collision center so I'm constantly working on cars and I see a lot of rigged up crap come in.
That being said, take my advice or others to tell you it doesn't matter what you buy there all the same...well w/e find out for yourself.
And HIDs in the stock light housing will glare like crazy and I'm sure you will get plenty of people flashing you and not in a good way.
Last but not least the Kelvin range for HIDs.
I have 6000K top and bottom and it looks awesome, mostly white but a small hue of blue. The higher the Kelvin Temperature the more color out put but it's not as bright, thus giving the reason I stuck with 6000K.
Hope this helps.