It's always going to come to stack size. If you're saying 15 to 20 bb, I'm only going to be stealing from fairly late in uncontested pots, and only w/ better than decent holdings when faced w/ limpers. I'll stay this way til I get to below 15 BB. Then, it's pretty much shove time for me. As to my bet amounts for stealing, Late, it's usually anywhere from 3x to 4x.