Sit and go and the Kelly criteria

[BillC]

But that 20-30 buy-in rule is based on the Kelly criterion.
Whether you like it or not, your choice of stakes is based on some estimate of your win rate or SD (unless you are overbankrolled or risk-loving). It is probably better to err on the conservative side and use maybe a 30-40 rule, since as you say, you don't really know your win rate, esp. when you move up.
I don't see why discrete jumps renders Kelly meaningless. In sit-n-gos, Kelly is maybe more relevant b/c of the relatively low SD.