Win rate is a whole different thing. 10-20k should be enough to look at your stats and say, for example, "I've only 3bet 1.5% of my hands over the last 20k hands. I should probably start looking for more spots to profitably 3bet," type of analysis rather than converging on your true winrate which probably takes more than 250k+. But, your game changes considerably over that many hands, especially if you are learning the game, so even then it's not a true representation of your actual ability to beat the game. Unless, you assume you haven't gotten any better and your opponents still play exactly the same. In my opinion, statistics are somewhat over-rated due to their dynamic nature. They are useful for spotting obvious leaks that appear w/in 10-20k hands, and fish at the tables, however.