Some high points in career winning percentages, open era
These calculations were done to find out at which point in these players careers they reached their respective highest cumulative career percentages. They are done at year end because otherwise it would take way too long.
Connors was still above 85% at the end of 1984, but his highest point seems to be the end of 1982. On the other hand, McEnroe’s career percentage was a bit higher at the end of 1985 than at the end 1984, which at first I found surprising. Also a bit surprising was that Federer's percentage has continued to rise with respect to what it was at the end of his best period.
Connors (through 1982) 859-138: 86.16
Lendl (through 1989) 851-144: 85.53
McEnroe (through 1985) 644-109: 85.52
Borg (through 1981) 605-112: 84.38
Nadal (current) 595-123: 82.87
Federer (current) 888-201: 81.54