[damaniac]

Your sample size over that time period is woefully indaequate to begin to conclude anything about winrates. In any event, if what the OP is talking about is playing less than optimally after a certain number of hours, then that might not well be the case in your example. It is probable that most people can play as optimally as they are capable for 20 hours a week, especially live. Now if you upped it to 60 hours a week, we might reasonably espect to see a decrease, over a large enough number of hands.