I recently harvested a grow similar to yours. I had mine in the little tiny starter wool cubes, and set them in about 3/4 gallon of hydroton. I Left them in the small tubs, and upon harvest (25-30"), I found that the root mass was very healthy and NOT completely filliing the tub. 1 gal per foot holds close for smaller soil plants, but hydro requires MUCH less root room. 3/4 gallon sustained 30" easily!
Ive transplanted babies TONS, and been mean as hell in breaking roots. After a slight stall, they always grow just fine. In hydroton, you got it made. I simply pour out what hydroton I can, wiggle the plant out, and repot. In yours, perhaps a little more effort to dislodge from the pots. Believe me, you can be fairly rough and they'll take it. I would worry more about breaking the stem than the little end roots. Hell, my last harvest, I repotted one 5 weeks into flower. Bitch went from hydroton to soil. It was a freak breed. It still a freak, but 3 weeks later its a big freak ready to harvest.
Under a 400w, if your plants are over 12" tall, they shoulda been flipped

' Hope i helped. Best of luck to ya!