iblaze...
1000 watts is ideal for 3x3.. ventilated perfectly... many people use a 1000 for larger spaces...
I saw a single plant with 1000 watt hps over head and 1400 watts of side lighting (14 - 100 watt enviro lights).. this plant was huge and trained very WELL.... it harvested 3.5lbs.. yes ONE indoor plant.. 2400 watts.. 3.5 lbs
I have also seen 17 plants under 2000 watts HPS harvest 5.6 pounds... a very tight set up with Co2, temp control, bucket system (w/hydroton rocks)
SEE picture
I also saw a set up with 13 plants under 3000 watts HPS and it harvested 6lbs... see picture...
Lower branches NEVER get enough light... growing plants taller than 12 inches before flowering is (90% of the time) incorrect growing, if maximum yield is your intention... (there are exceptions)
iloveyou