Saw the show and bought the book... It's a seven foot or larger box he's using. I've rented and used the 7 foot Wescott box and LOVE the results for full length fashion shots with low ratio glamour lighting. The light wrap is incredible. Here's a shot from my portfolio done the that box on an Alien Bee 1600 strobe.
I'm torn between the big octo and a 4'x6' rectangle. I've used both and I prefer the octo. I may have to pop for the big octo right now if it's on sale. Is that on the B&H web site or did you call for a special price? BTW, the build quality on the Wescott box is superb! I've used many different manufacturers softboxes, and I've not seen one better constructed.
Here's a full length standing shot where the box was only 4' away from her.
I also have a 48" octobox that is good for about 3/4 length bug no more. The light falloff when you get the box close to the model is too great at the knees. You can really see the difference.
Thanks for the information!!! Good luck.