Bigger bulbs for HPS

I bought a cheap outdoor HPS setup with a 70W bulb. Can I buy a bigger bulb for this? Will my fixture support higher wattage? Could I buy one of these newer CMH bulbs? I am veging right now and experiencing slow growth. I know I have low wattage right now, but there is only 4 plants. Would I be better off buying some CFLS right now to get me through veging, or will I need higher wattage anyway when I flower. I will Probably only flower 2 plants.

the ballast needs to match the wattage of the bulb.

A 70 watt HPs can work for 2 small plants. You should ONLY use the rated bulb in you lamp. Don't use a bigger bulb or a metal halide bulb in your lamp, it will likely not work and there could be a potential fire issue. You can always get a 42 watt CFL at Home Depot with a reflector to supplement your HPS and I would be doing that in your situation.

Play it safe!