its all about the penetration imo iv read that denser buds are coming from 400hps than a single 315cmh. i have the hydrofarm 315 setup used it in veg but i would trade it for two 400hps ballast anyday. i also have 600hps and 1k hps. Maybe ill run side by side my 315 vs my 600hps but i dont think it would be to fair on the single 315. The 1k would absolute rape two 315's imo. The 1k will produce long hard colas so dense you can throw them through a window.