How far down can you top a vegging plant?

I have a couple moms I wont be needing for a while and istead of having to raise my light for them I was thinking of just cutting the plant so many nodes down at a suitable height. I have 9 plants 6 of them going to be mothers counting the 2 overgrown orangebud mothers all under 400 MH.
Any Ideas?

You can cut all but 1 or 2 nodes off, IE top the whole thing but 2 branches. I warn you they get awful bushy afterward and grow out more than up, I get my best results by chopping the plant in half on top and on the roots. Yes I cut the roots off older moms to keep them smaller, otherwise they outgrow my room in 1 month. This is hydro of course so dont cut roots if in soil obviously.

lol I can see someone pulling their plant out of the soil and cutting the roots right now lol