Greetings, even though i'm not that " experienced " with the indoor grow,
i've done an untouchable amount of research, which has put me on the path,
of an amazing crop. So, i want to congrads you, on your set-up. I believe you
have a great set up going there and would suggest going with the 600w HPS.
Cuz'n you have just a bit larger space than mine and i run the 400w HPS for
this flower phase.

You can get that set up with the new Digital, ( dimmable ) ballast for under
$ 175. If you need the website i can look it up for you. That research
( price comparison ) took me hours, so if you' re interested i can find it again!
The beauty of the these new ballast is, they run cooler, the warranty is awesome, you can lower the output if you are working in the G-Room,
If you run the lights during the day and run into a " hot week " you can
also combat the heat by dimming the power out put ! The plants don't mind !
Running the lights at " night " ( off peak hours )
should save you, $$ / month too.

Zeffer