You can train FTs during the Playoff for 2-3 weeks. The big advantage is that you can play the playoffs without any constraints on the training. And if you are eliminated you can train all your team with only 2 games per week. And we will know :p
The french managers have made a little study about the potential. And there were many players (centers I think and of course all-star) who have reached 70k-75k without any slowing. That's why I wonder if there are (or not) decimals in the potential...