An HPS with a blue spectrum such as the Hortilux HPS with blue spectrum would be the best way to go IMO. Test has shown that just a small amount of blue/MH light in the bulb will help to stop stretching. Also, hands down the most lumun will give you the best outcome time and time again. Also, I would only use Hortilux bulbs on a 600 ballast, they seem to have a longer bulb life than other brands when it comes to the 600. A 600 MH and 600 HPS is over kill IMO for a 3x3 area and you will have allot of heat issues as well. Done right you should be able to produce a Lb with a fair strain and a handle on your feeding schedule.
I haven't read the second page of this thread so, some may have said the same thing already, or completely contradicted my info, but you can easily confirm or dis confirm my input.
Adieu