fwiw, I'm on my 1st grow....................
DR120II tent, I started with 4 bulb T5HO's, added 2 125w cfl's, and then removed those and put in a NextGen 400w/600w ballast. I used the 400w setting with a MH bulb and things really took off. ( maybe they were getting ready to take off anyway????) I love the Nextgen
I switched over to 600w setting and put in a HPS bulb for 12/12 flowering.
BUT, with the HID lights, you'll need to vent (air cool) them out of the tent to keep the heat down.
Anyway, good luck with your grow,