what sort of venting system do you have/are you using?
You can hurt your plants pretty bad with too much light - not to mention the heat produced from it. Most of the suggestions in this thread are solid. Like I said, I have a 3'x3' tent with a 600, I vent directly outside, and have no problem with temps or fresh air flow.
If you have to vent inside for whatever reason, and use an AC, or even open window to get/release air, then maybe a bigger, hotter, light isn't the answer.
But I would still probably get a bigger tent, for future upgrades. It's nice to have all that room if you can fit it somewhere.
Goodluck mate!