Well, it's not actually the leverage you take, but the size of the bet, right? I mean if you bet 10% of your money with 10X it is the same as 1% of your money at 100X. But yeah, I agree, 10X is certainly adequate. Maybe 20X for more experienced traders, but you should never need 100X. If you do, then you are probably trading too big. The kelly criterion (http://en.wikipedia.org/wiki/Kelly_criterion) says there is an optimal bet size (any bigger and it will take too long to recover from drawdowns, smaller and you will grow too slowly). This optimal bet size is based on your expected return and your probablility of success (ie optimal for beginners is a smaller bet size as a percentage of the total portfolio than optimal for higher probability/expected return traders). It took me a few hours to break the kelly's paper down, but that's the jist of it.