If that isn't a loaded question....
I have a mars II 1200 in mine.....
@BigSm0 said four of his autocobs are good for a 4x4 (if I was buying new lights right now....that is exactly what I would be going for). There are T5 lights that do very well in that area...but the fixture is almost the same surface area as the tent floor (they're big).
Long story short.....if you're looking for wattage.....no less that 600 (or the equivalent to 600 in the case of the cobs) all the way up to 1000 or more. Heat will be an issue, depending on your setup.
Hope it helps.