well im assuming you can light either the mh or the hps, or both at the same time. i would be weary of that fact. if they both come on it may be a heat issue if they can be switched on and off seperatly i would get the mh and hps, becuase u cover both vegg and flowering. and 400wtts is mucho for a cab. also if this is just for flowering, the mh is completely uneccessary, and a 400wtt hps alone may be enough.