whoa, WM, you top the plant just when she's switching? I guess that puts the growth spurt to the lower branches all right. I've always read to top during veg, and allow a week to recover before putting into flower.
Vic, right now, I'm growing some 3 foot plants, and they have 2 sqft each to grow in. So I top them once, when they are 5-6 inches tall, by removing only the meristem, the tiniest piece of green, the little part between the smallest new leaves. If done well, that will result in a perfect V in the main stem. Several side branches will grow up to become big budders, too.