I'm sure you have heard of the 300bb recomendation for a bankroll. I think this is a very good rule and keeping only 40 in there may not be such a great idea. I think learning discipline and keeping a bare minimum of 300bb in the roll and allowing it to grow is the best course of action. Making plays out of fear of crippling ones bankroll, in my opinion, is a horrible strategy. Learning to take control over your tendency to loosen up as your bankroll grows would be a step towards making you a much better player and building your roll would allow you to move up to higher limits in the future.