50-100 is probably what some players keep, but I've never done that. I've always run around 30 BIs or so, and if I get to the point where I'm down to 15-20, I can move down. At my lowest I actually had dropped to 17.5 but at that point I was saying **** poker, and was actually casually hinting to the guy who staked me before that I may need one again soon. I'm not super proud or anything like that, and the guy that staked me made a nice profit also, so I figure I'm doing him a favor too
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Anyways, clown is right. It is pretty aggressive, but I think given that busto won't ruin my life, I feel the risk of playing with 25-30 BI is worth it for the extra amount of money I get playing at a higher limit.