Its hard to say without knowing which exact pheno you have... I grow Blue Dream from HSO (Humboldt Seed Org)... She is fairly short, very stocky and robust... I would say that if your tent is 6.5 ft high, you got about 5 ft of growing height to work with... I would grow them to around 18 inches.... Top them.... Let them go a few days longer till they are @ 20 inches... Then Flip em.. It is a fairly easy grow, and a VERY large yield... However, make sure you lollipop the crap out of them, and they suck to trim.... But I just pulled 12 Zips off each plant with 2 under a 1000....