I have a 600 watt HPS/MH and a T8 8 bulb setup and a smaller t8 6 bulb setup. The 600 puts out crazy light but the 4ft T8 8 bulb setup puts out a little less. I have also used cfl's and i think the T8's blow cfl's away and less heat. But DarthD3vil is right, check out peoples grow journals and the pics of different grows using the lights your considering getting.
BigBudE