Metal Halide (MH) have a much more blue spectrum, they are good for vegging. High Pressure Sodium (HPS) have a much more red spectrum, they are good for flowering. So those who are using a MH for flowering, you are using the wrong bulb. Get yourself a HPS.
That being said, I did the math for the cost of CFL bulbs and the amount it would take to have a decent yield. With the bulbs, reflectors, and the connections, it would be cheaper to get yourself a 400 watt HPS from HTG Suppply on Ebay, and you'll get much better results. Not to mention is will save you the hassle of wiring all the different bulbs correctly.