Hey fresh, i'm running a 250 hps in a 2x2 ft area giving 7,000 lumens per sq ft and have had no problems. The only problem I'm aware of with too much light is bleaching of the leaves, if that happens just move the light a little further away!

You really only need to be concerned with proper ventilation, but there's very little difference between the 250 and 400 in terms of heat, you're gonna need a good extraction system for either.

Good luck!