Hahaha, damn you, autocorrect!! No worries, man. Thanks for your replies as well! I'm happy to be of help! If I can manage it, I'll post you some pics of what I'm talking about here in a minute... I've been growing for years but I'm new to posting on forums! I don't even know how to add pictures yet, but I can tell you anything you need to know about SCROG!!
So, as far as yield goes, this is of course one of "those questions"--i.e. the type that always gets asked, but that is always hard to answer because it's so subjective, and so contingent upon a number of factors... That being said, if you are rocking a beefy strain like Heavy Duty Fruity, or a nice Kush cut, as is the case with your grow, you can expect a FAT yield out of this set up.
15 oz per plant is definitely feasible from this set up, provided you give it the right kind of love. Those 15 gallon pots are soooo awesome for a SCROG like this too. You can fit 2 of them into a 4x4 or 5x5 space for sure, but my current set up is just one plant in a 15 gallon pot, right smack dab in the middle of that 1000w HPS. The canopy filled out just as I described it to you, and now I have this awesome table of buds...
I've grown in a 4x4 tent for a couple of years now and I absolutely love it. The corner posts make perfect SCROG anchors, and I routinely pulled 12 ounces out of this tent during my formative stages... If you've got some experience, a nice Purple Kush cut, and a healthy and balanced nutrient line, you can definitely push 12+ ounces a plant out of this set up.
As far as starting the SCROG from a single towering bush and turning it into a table top versus starting it as a baby and weaving it into a table top, I can't really say which is better per se. The end result is essentially the same; you end up with a table top of buds all receiving even distribution of the most intense light. I would venture to guess that your internode spacing would be tighter in a plant that is grown in the SCROG from its earliest stages. But, a plant that is grown straight up and then snapped over will have much stronger support stems. Plants that are scrogged from the beginning tend to be really stringy and bendy. When I've grown plants straight up and then bent them over, I've still filled the screen out to the point that it blacks out anything below, and I've had bud sites pop up every couple of inches...
In short, I really haven't seen the benefit of putting a plant into SCROG right from the beginning. I prefer to grow her up, and then snap her over... Pictures soon to follow...