Well, it looks like you are working the shit out of them, so even the ones that have stretched can be easily worked back down so you can still get those plants to maintain a nice even canopy during flowering. Anyhow, if one set is stretching because the light isn't as powerful as the other, just lower the light to stop the stretching. And if you only have those two lights, to flower them, then start light rotating them daily. What I mean... say I have 4 plants and I have 2 under 1000, and 2 under a 600, then I would get 16 paper clips, (4 set of 4 different colors) and put one at 12 (blue), 3 (green), 6 (red), 9 (yellow) o'clock on each pot. Then I would rotate the four plants each day like so...
First create 4 optimized marks that best light up those 4 optimized marks, (2 under your 600 and then 2 under 1000), then move the two plants that were under the 600 yesterday, and move them so they are under 1000 today, and then move the two plants that were under the 1000 yesterday, and move them so they are under 600 today, then also rotate them 90 degrees and mark which paper clip you are on in the rotation everyday, and then all your plants will grow evenly helping them to all produce the best yield you can achieve using what lights you have available to you! Yep, I have been there and done that way to many times, LoL!