I don't think there is any change in training until player get 5th star, but there is change after 5th star, slower 10% max, not 1/3 as u said... Maybe its 10% more after player get 6th star, but I don't have any scout to confirm that
Btw, if u use hard training, it does nothing better than normal training. Hard training only doubles skill progress for double amount of condition, but chances of injury are greater than in normal training. Hard training only reduces time... You may click practice match once in hard training, or click once in normal and wait an hour to click it once more...
And yes, one more thing... there is no difference between normal cardio training and hard stretching training... u get the same range of skill progress and use the same range of condition (6-8)...