For drifting I would set the Chart Speed to its lowest setting. When the motor is running try starting with a setting that equals the mph the boat is moving at and tweak it from there.
For the different water depths you should start with 2x to 3x the water depth all depending on how far out you want to see under the water. The amount of detail you want to show should also influence this as well because the farther distance you show the less detail it can be shown in.
All other settings are really user preference as some can see one color better than another, some like higher or lower contrast and sharpness settings. Make a Sonar Recording and try adjusting the various settings while on dry land and see which you prefer.