Well, if you look at my journal, you'll know I don't play small!
I've never vegged a plant only 4 weeks, even from clone LMAO, but I do love them large. A rule of thumb told me has always been grow them to 2' and flip, they'll double in size and you'll be happy....I wasn't, so I sometimes go to 3'. However, when vegging longer, I've noticed the gals stretch alot less than if I flip earlier.
Check out the last few pics of my journal and you'll see a group of 5 1/2' monsters in the background...those gals were taken to almost 3 1/2' before flip! Tons of buds top to bottom, too bad the bottom buds will only be good for hash!
Of course, some just don't have the headroom to go large, some prefer short...it's all in your preference and desires! No one way is wrong, that's the beauty of it!
Just my observations and HO
ps....I have a rather lanky 6' PE gal in there, she is bent over with weights tying her down (you'll never figure out which from pics lol). She's covered with bud bud and more bud, I'm beginning to think she may just rival the 10oz Kandy Kush plant I harvested...would be great to have several oz of PE from a single gal!