Minimum_reuse could be increased to 0.1, or even 0.2.
For adc_bailout, you could use 1/64.
Note that these settings will degrade the quality of your image.
Also, I can't recommend using a count of 20, as the results will be
quite splotchy. However, increasing it will slow your render down, so
that's not exactly what you're asking for here :)
...Chambers