OK, so you're talking about buying two ballasts.

HPS 600 great for flower.

Get a 400 watt halide system- very few halide bulbs @ 600 watt, loads @ 400 and 1 K. 400 veg is perfect to feed 600 flower.

600 watt halides in N. America are rare and pricey- almost always a retrofit to a hps system. Go w/ the 400, pick up the Hortilux Blue halide- gonna be severa hundred dollars cheaper.