With your hourly rate and standard deviation, 300 bb would allow you to play forever with less than a 0.1% chance of ever going broke, but this is based on never spending anything.


[(1-1.8/12.5)/(1+1.8/12.5)]^(300/12.5) = .001


If you always spend 1.8 bb/hr, then you have an hourly rate of 0, and you will go broke with a probability of 100%, though it may take a very long time. You could spend .8 bb/hr and you would still have a risk of ruin of 2%. If you only spend what you make in excess of 300 bb, then it still depends on your average net win per hour after spending, which I suspect should be close to 0 since you would normally be above 300 if you didn't spend.