Your lights are correct for your space, and you have another choice, which is to replace the HOODS with ones that may be air-cooled. They are GREAT!
Also, if your ballasts are in the same room as your plants, put them somewhere else- a ballast makes a LOT of heat.
I would not recommend replacing the light you have with either of the configurations you suggested. You will still have heat problems with either; a 600 is not much hotter than a 400. Air cooling the lamp is the most efficient option.