I have used 750 watt ballasts in the past. I had about 4 runs with them in 3 gallon coco pots. I had 18 plants in 3 gallon geo pots and let them veg for a month. I was growing og kush and used the scrog method. I pulled 1.55 lbs per 750watt light of high quality medicine using H&G. Those 750's got stolen so I decided to upgrade to 1000's. I growing the same strain of OG using the same 3 gallon smart pots and giving them the same veg time. With the 1000's I have about the same yield per light. The quality is a little better with the 1000's and my lower bud sites get hit better by the 1000's and harden up more(less fluff) If you use the 750's this can be solved by first chopping your tops and let the lower bud sites soak up that light for 4 to 5 days. So in my personal experience I got the same yields but the 1000's produced buds that were a lil more connoisseur. But who know maybe im just not rockin the 1000's to their full potential yet. O yea. I have ran 600's in the past also and always got 1lb per light consistently but the difference in quality was noticeable.