maximum yield i would say 1.2 Grams per watt but i dont think you will get this much. experienced growers tend to get about 1g per watt of light but its not such a easy thing to do

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For your area i would recommend more light. have a friend using the same setup and he have problems with stretch. If you want to MAX that area you will need at least 1600-2000w of HID lightning.
And a good yielding strain with a good pheno is also important.
Only time i heard of people getting higher then that is people who have vertical grows. i dont know anything about doing it tho but some guy named heath scored 2.5 g/pw... using a critical mass but still thats insane imo.
When growing you should nevr expect a certain yield. Trust me it will usually mean you will get disapointed. At least dont excpect anything untill you know the plants you are growing in and out.