I just picked up some XtraSun hoods for $60 a piece, digital bulbs for $60 apiece, and Lumateck dual 600 for $290 a piece.Get Super Sun 2 or Radiant reflectors and lumatek or galaxy dual 600 electronic ballasts, you will be gold!
(the hinged glass on the radiants are so nice, easy to clean and change bulbs etc.)
Where do you get the idea that the 1000w is more lumens/watt? 600 watt ballasts have always been more efficient. They are rated between 92-95,000 lumens whereas the 1000w is about 145,000.so you went with 600w, I was going to say the following
600w offers more coverage of more plants, but 1000w offers higher yields on fewer plants.
6x600w = 3600w, 4x1000 == 4000w, and 1000w also offer more lumens per watt. However, without an airflow system or two in 4 1kw lights, it may be too hot.
The thing is tho, it is more sensible to make smaller plants and get them to maturity faster and yield more so 600w was probably a good call.