I don't know how much of the thread that you have seen/read but I think that with such a small area, it's going to be a matter of preferance. I haven't done a grow with my 400w or anything more than CFL's for that matter, but honestly, it's all about lumens per square foot. You can never have too much light, but is it worth the extra money on your light bill every month? A good 400W will give off about 55,000 lumens. You could also add some sub lighting like strip CFL's for the added lumens and side lighting. That's what I plan on.
The sun will naturally give off about 10,000 lumens per sqft. My stealth armoire will be 4x2x6.5. That's right at 8 square foot or 52 cubic foot. You only need about 3000 lumens per square foot but ideally and closer to perfection, you want 7000 - 10,000 lumens per sqft. With my set-up, I will have about 9000 lumens per sqft.
(4) 4ft 54W 3000k Sunblaze CFL's in the corners (that's about 20,000 lumens) and a 400w MH (about 55,000 lumens) for Veg. I am using the CFL's to give a little more multi spectrum of lumens.
Then I will use (4) 4ft 54W 6000k Sunblaze CFL's in the corners and a 400w HPS for flower.
So do you really need to go to a 1000W ?? I think not.