[jtcchan]

> It's not difficult to reach 90% confidence with very a small sample size:

I think the difficulty in reaching 90% confidence is in designing a challenger that is THAT much better the original (i.e. 10 vs 5). Most split tests are shots in the dark. You'll basically need a design or copy that is doing pretty bad and an a challenger that is a lot better (but not obviously good enough that you use it in the first place).