Win or loss is irrelevant to when to stop or not. The correct answer is where there your EV drop or suffers. Prime examples are when players flock to the table, bad penetration etc. That being said it is unwise to totally dismiss your current win loss for the session and how the pit perceives it. You often hear people express concern on a casinos "win tolerance," but the fact is that big losses catch attention as well. Losing big in short order (which normally requires large bets) and then being seen betting just single green chips for extended periods show the casino you are varying your bets. Also if they suspect you of counting then they now know you appear to be well funded, even worse is if your comportment is seemingly unaffected, large losses like that ploppies usually get visibly upset....(hint hint) Normal ploppies dont sit down, dump 3k and then bet just 25$. The normal pattern i have noticed in my experiences in ploppies will start out small, hit a streak of wins and then start pressing their bets and run up a large win. Never have seen the reverse, where the ploppies runs up a huge loss and then bet a wager that would be nearly impossible to achieve a loss that large.... They might lose their few hundred they started with and walk away. Ploppies are not there to grind it out at the BJ tables, they rely on "luck" to put them on "house money" and they feel better about playing after that point....

If your store frequently sees you win and lose the amounts you mention and seem comfortable with it, you probably have nothing to worry about. If your losses affect you mentally and your playing suffers then by all means stop playing.....