I am speaking in feet and inches, Bluberry, yes.
Hiboy, this is what I have found/experienced. If you're putting out seed-starts, they will get HUGE. For me, uncontrollably so. But, if you're starting with clones, at about 2'-3' tall, put them in the same space and they'll hit about 5'-6' instead of the consistent 10' I'm getting. I'm only 5'1", so a 10' tall plant is HUGE for me and difficult, if not impossible, to work with.
My seed-starts that hit that 10' hight have approximately a 7' spread, it's definitely wider than my arms can reach, but not twice as wide.
Blaze, you have room to work with. Remember, I only have that 3'x16' planter, so i do kinda cram them in. Interestingly enough, the first year I grew in this planter I planted 11 girls (split between seed and clone starts) and I got about 10lbs, give or take. This last year I put in 8 plants and I'm going to guess that I've gotten about 12-15lbs. I suppose that would bear out what you're saying about giving them room and they'll produce better weight, yes?
The difficult balance for me is this: I prefer to start seeds to do a first run outdoors in organic soil. I feel this allows me to gauge their growth habits, overall appearance, etc. But I have to start many seeds, and then when I end up with a bunch of girls I don't want to kill any of them, and so then I end up with a lot of plants that I need to fit down there because growing OD in pots is a pain in the ass. Literally.
Quandaries and conundrums, they abound!