I agree basically with what khris is saying. A dud will always be a dud, a superstar will always be (programmed to perform like) a superstar. Matchratings are key indicators for all players, except attackers, they only need to score goals and will most likely keep doing so in similar circumstances.The really good players are so well programmed it trumps quality, these players will outperform players 2 stars up, so quality doesn't mean everything, The more stats (matches played) the more reliable they are of course. I usually need 4-5 matches. for me a 7 is as low as I except, a 6 is a liability, especially in defence.

I don't agree with testing vs low lvl teams, The difference in Q is so big it overrides the subtleties in the game mechanics. You might find the best players in your squad perhaps, but have no way of knowing how they will do against evenly matched opponents. If you want to test your team, play against more evenly teams. Now I don't friend people from my lvl, so I sometimes play teams 1 lvll up. Then you will know where your weaknesses are, they become more clear with a loss then with a 10-0 victory over a 1 star team. I mean what does it say whether it is 5-0 or 10-0. Or FA friendlies, but wee bit unsure about those as of yet.