i am center scout of germany for some season, so i have seem many players and i also would go for a lower salary when they reach the cap but with ~50k salary it become ugly ;)
There are also some other factors influencing this "border" so it is hard to tell exact values, because sometimes the training seems to be normal because of higher sub etc.(so you got still your skill ups in normal time, even if the training effect is reduced) and the subs are also in the salary formula and the weights are "maybe" slightly different to the salary formula(especially blocking for centers seems to be more important for potential).