150 would be sufficient. Check out the thread (My 150 HPS cab) under this. that might answer some of your questions. A 250 would be better though. More light, more yield. Its really up to how much you want your electricity bill to go up. If heat is not a problem then I would go with the 250 for sure. Speaking of heat not being an issue you should go with a 400 watt HPS with a MH conversion bulb. That would get you some nice yields and you would have the proper spectrum for veg and flower.. Check out Justaseed's scrog posts. Now those are yields you just cant get with a 250. Add some supplemental CFL's at around 3000k if you go with the 150 or 250. Good luck. Peace