250 watt hps VS. cfl

Well here is my question and i hope someone can help me out on this.My last grow was northern lights from nirvana seeds wich by the way were of excellent quality and turned out awesome.The problem with my last grow was I only had 2 42 watt cfls lights for growing and flowering.Now that I figured out how to grow without messing it up I purchased a 250 watt hps light and I was just wondering how much more of a yield I will increase with this light.Last grow I only got 17.5 grams from one plant that was about 2-3 ft tall.Thanks in advance