which light for 3x3 tent

I'm starting my first grown when my stuff gets here. However, I'm still on the fence about the light. Here's what I'm working with

I have a 44x46 closet. I'm going to use a 3x3 tent and there's a hole in the ceiling to the attic. perfect for venting. The plan is put 4 plants in at a time.

Should I use a 400 or 600 watt grow light? Here's my options...

400: http://www.amazon.com/Apollo-Horticulture-GLK400CT24E-Digital-Dimmable/dp/B00547I5I8/ref=sr_1_3?ie=UTF8&qid=1373507420&sr=8-3&keywords=400+watt+grow+light

600: http://www.amazon.com/Apollo-Horticulture-GLK600CT24E-Digital-Dimmable/dp/B00521B894/ref=sr_1_1?s=industrial&ie=UTF8&qid=1373507479&sr=1-1&keywords=600+watt+grow+light

The reason I'm using a tent is because I rent the house and I want to respect my LL property as much as possible. The house is spotless inside and out, bills are paid on time, and everything is in order.

Is the 600 light worth it? or will I have diminishing returns? I should mention, I have a tower fan and a couple of small personal fans for passive air intake. I'll also open my window for fresh air, and my bedroom has a lock on the door.

600W is the most efficient HID setup you can get.
More lumen per watt than ANY other setup.
I started with a 400W.... and I still use it.
But it's nothing compared to my 600W...
the biggest thing I would recommend for a tent setup is the hood enclosure..
you can vent the light heat out with the hooded setups so easily.
Without them...it get's hot pretty quick..no matter which wattage you have.

you can get that 600 watt setup for the price you'd pay for the 400 on E-bay with free shipping at mega-low-mart for 134.98$ http://www.ebay.com/itm/Apollo-Horticulture-600-Watt-600w-MH-HPS-Grow-Lights-Digital-System-Set-/171015859655?pt=LH_DefaultDomain_0&var=&hash=item6d7c9ec095 . I'm working on basically the same setup got a 3x3x7 tent 6" fan and filter just need to get a new light.

I second what he said. watt/watt a 600W HPS is more efficient than any other HID.. meaning more lumens/watt than a 1000W HPS. I advise you to get the 600W with a dimmable digital ballast.

600for sure, but you may need to rethink your fan situation. get a good inline fan, not a duct booster.

If you get that 600w dimmable ballast you can turn it down and run a 400w bulb in it if you have heat issues so best of both, but if you buy a 400w you cant turn it up to run a 600w

600w hps and you're winning.