I'm currently trying to be able to do the middle splits, left leg splits, and right leg splits before surgery.
My real concern is not how much I can physically lengthen, but leg to body proportions. If you go to Dr. Paley's website and see the Asian girl who did 16 cm, that's too much. I'd love to be 16 cm taller, but not if my legs looked like that, and if I did it they would probably look even worse. I have long legs already.
My current thought is to do 6.5 cm, and stay less than 2 standard deviations from average.