What I think is that most or maybe all of the altcoins might reach the ATH peak as we are nearly approaching the bull runs. In these bull runs, bitcoins will carry most of the popular altcoins along and they would travel to the all time high peak so far. But it might be difficult to redirect you to top few coins which can grow by more than 50x.

Most of the coins have already started showing us some growth but yet the limit you kept is quick high and I do not really think that many of the altcoins would cross more than 20x. Even that is a higher amount and I could only place it because you already have a more higher number into your mind(50X). You should try to explain your mind that it might perhaps be not possible or maybe only 1 or 2 coins might make such huge growth.