mine usually end up averaging a bit under 3 feet. this current batch got away from me and even after bending them over and topping i'm still over 3 foot tall for most of them and i think they will stretch a bit more. although i've had a few small yeilds from my 600, that was due to me messing up or trying crosses that turned out to be poor yeilders.
my first 3 yeilds and my last 3 yeilds have all been great under a 600 but next time i'm going to work on keeping them shorter. i want to see what it looks like if i only let them get to be around 2 feet tall. i end up cutting much of the bottom stuff so it's a waste to grow as tall as i do and a bit of a pain with a 600. i do love how they look though.
i've decided to top (something i rarely do) and super crop (something i used to do but stopped), to keep them low and wide next time.
as far as watering goes, i use a count when i water. i start pouring and count. a 40 count will over saturate a 3 gallon grow bag. i sometimes only give them a 25 count due to lazyness or i want them to dry out a bit quicker. i pack way too many plants into my tent though, which is why a few on the edges don't dry out as quick as others unless i rearrange them every couple of days. i'd much prefer to whip up 6 gallons of nutes than 9 or 10. i'm really lazy.
i used a 1000 watt for most of my grows so being a bit under 3 feet was fine. oddly enough, it still seems to be ok, i just want to see a shorter grow for once.
do you guys saturate your pots on each watering/feeding? you'll do a face palm, but i rarely water until 10% or whatever leaks out. 16 or 17 oz each of the last 3 grows. what can i say... lol