i also tried to play a bit with the rest packs. i tried to see if giving rest packs to exhahusted players before the game do change how they form. but it's really hard to tell how the players would have done without them. however i've noticed that player that were in low fatigue and were given the rest packs did worse in ratings than players that have been in good condition from the start.
but it was more of a slight than a clear trend.

It surprised me, but i'm beginnig to think that the player's condition value during maintaince is the acctual value to be used by the match engine.