How many plants could I fit in new tent?

I've got a new grow tent kit coming at end of week, Its a 5x5 tent, which comes with a 600w dual spec an digital ballast that goes up to 660w, I've bought another lighting kit the exact same as the one that comes with kit..so that will be a total of 1320 watts.. I just wondered how many plants i could fit in it? And also how much could I expect to yield? I was thinking between 6-8 plants?