I would not do it - 1000w halide has short life, and loses brightness very quickly - 600w HPS though is an excellent choice, especially with reflectorized lamp - or the venture 575W pulse start halide - the 575w psmh
http://www.venturelighting.com/LampsDataSheets/NaturalWhite/95577.pdf runs 575 watts but is the equivalent of 2 of the 400w you mentioned. The lamp is designed for sporting football field baseball diamond illumination etc., but works fantastic for growing.

Here is a link that might be useful: Venture makes super good lamps for growing