Cholo- 7 cm is normal. Not a lot seem to actually go for, or achieve 8 here for one reason or another, but if it is your goal and your nail doesn't fail theres no reason you can't do it.
Don- All I know is that there are reports of knee pain from various people who have had rods inserted in their tibia. The other reason is the much higher complication rate. Keep in mind most complications don't really have much to do with the amount you lengthen. Having personally seen someones screws coming out has really left me biased against tibias. Research the knee pain and see if you are willing to risk it, then save up a lot of money just in case, and hope you don't need it.
On the plus side tibias are much more comfortable than femurs- every single person I've met doing femurs has a terrible time sleeping. The people I've met doing tibias sleep like a rock for 8-10 hours. The stretches are also less painful to my understanding.
My days are the same over and over- wake up at a crappy hour, force myself to eat breakfast, depending on when my PT is either try and sleep again, or hop in the shower, do PT, come back and rest for a couple hours, head to the pool or get dinner(order may vary), head back to room and shower again, browse internet, stretch, take zzquill, try and fall asleep for hours, sleep a total of 2-5 hours on and off. Repeat.
Towards the beginning the routine was spirit crushing, because early on my sleep was especially bad and accompanied by borderline hallucinations as I mentioned before. My discomfort was very high and I couldn't even focus on watching a show or reading properly, and the loneliness was certainly present, which I had initially thought wouldn't be an issue at all. The whole first month was a battle to not give up, with lots of ups and downs. During the day while I was with friends by the pool or at a cookout, or at PT I felt ok and strong, but each day going back to my room was like death. I've heard a few other patients who have done this alone have felt exactly the same, including one who couldn't take it.
But it does get better. The second month was quite a bit more bearable, and although I am weary from all this now, the fact I'm at the end of the road is keeping me going just fine. For anyone doing femurs you really should have someone with you, especially that first month- I am strong mentally and physically with a high pain tolerance and it was extremely challenging for me. For tibias, because you won't feel tortured and will be able to focus on things as a result I think you would cope a lot better. Also just the fact you will know you only have two months instead of three will help, since just the fact I had three months of lengthening really wore me down when I was at the beginning.