400 watt HPS to big for 3X5X2Ft ???

I plan on building a custom grow box that will be 2 feet deep, 3 feet wide, and 5 feet tall. I will be using a 6in cool tube with a 4inch centrifugal (175cfm) fan. I'm wondering if 400hps would be to big for my box? I know i could run a cool-tubed 250 with no issues ,but i would prefer the 400 for the yeilds . I plan on growing 5 auto-flowering ak47 and blueberry plants. Also, Do you think i could get away with making the box four or 4 1/2ft tall??
Any help is greatly appreciated

The 400 wttter will cover a space of 3x3. the height of the box being 5 feet would be good dont forget to acount for the height of the pot and distance between light and plant. The watts per plant i have heard would be about 50 to 80. I grow 6 under a 400 watt check out my sig.(bottom of screen)

I got 4 under a 400 W hps in a 3x3x5 space with no problems.

CK