Way overkill. I'm running 1000 hps in a 4x4 and its basically overkill. I've done 2x 400's in a 4x4 before and thought it was great, and if I had a 4x8 I would run 2 400's, one on each end, and a 600 in the middle.
You'll need a lot of airflow, both active intake and exhaust. It's not for the...