Look at my gs - its been that way for 10 seasons, the worst I had is mediocre on any player - because he got injured for 2 weeks - I rarely get average. The funny thing about GS is that it can increase suddenly even if it is low. 48-75 min per week is still ideal, sometimes exceptions happen. If you have Proficient GS on any player you can go beyond the 75 min but over a 100 minutes is asking for trouble.
This surprises me.
In my experience, playing a player with 9 GS more than 70 minutes increases your chances of dropping to strong to over 50%.
However, this isn't too much more than the odds of dropping to strong in any other window between 49 and 70 minutes, which is usually around 45% or so.