The general "rule of thumb" is around 50W/sq foot with HID lighting. You can use more light (up to a point) if you can deal with heat, etc, but less light will almost always affect the end result. Also, most hoods reflect best in a rectangular pattern so, personally, I like 3x4 for 600W and 5x4 for 1000w. If you scale using those "per light" areas, you'll have better results. Also, all lights are better in the center vs the edges but it gets worse when you're not running enough light per sq foot.
donutpunched: 3Kw in a 5x8 should be great, maybe your hoods are turned the wrong way or otherwise not placed properly?
arizoning: 4x400 in that area is just a little bit of a stretch, depending on orientation.
Like I said, plants always do better in the middle than the outside but not enough light compounds the problem.
