blackbeltusa has the right concept; a monster plant won't do you much good without the lighting to flower it.
You basically have a 400w light; that is not near enough for a monster plant. Consider that the effective depth of your light is 3 to 4 feet, and at 4 feet it's piss-poor - even at 3 feet it's nothing to brag about. Now consider that your plant is going to triple in size during flower (for certain with a 400w - the less light, the more the stretch.) Now, if you grow the plant in veg until it is 2 feet high, for example, it will hit at least 6 feet during flower. With your lighting you will only effectively produce (good) buds at the top 3 feet of the plant. So, you spent all that extra time in veg for nothing. Get the idea? You could veg to about a foot, end up with a 3 foot plant and still get the same yield, more or less. On top of that, it is difficult to maintain a healthy plant when it is a monster and you only have lighting for a 'normal' one.
If you need more explanation let me know, I'm in a real hurry here and typing like a madman. LOL By the way, the above is very much an example, the variables are huge. Some sativas grow 4 times their vegged height in flower ... and that's just the beginning.
Really gotta run ...
FYI - I use 2 x 1000w HID lights and veg at 6 inches - SOG style grow - with a strain like White Widow that I am growing now, 4 ounces per plant is a realistic expectation -
4 ounces vegged at 6 inches. See what I mean? And my veg time is less than a month from seed. I suggest you rethink the monster idea too, but that's just my opinion. There are thousands of others.