Firstly, I think the range for gameshape minutes is about 48 to 75 minutes. Playing 79 minutes constantly will decrease gameshape rather than increase it.
Secondly, I agree that the ideal range is around 60 to 65 minutes.
Massage specialty (in my experience) allows you to play around 80 minutes without experiencing a big drop.
I think the massage specialty allows you to play about 3 or 4 minutes extra with no harm on gameshape. Playing 85 minutes a week is too much, even with massage specialty.