RE: Question on my 9C using Hitec digitals and rates, etc.
100% in the dual-rate screen gives you full end-to-end travel your stick is normally set to give. You usually then set the lower rate.
If you are programming servos, you can set the EPA as high as possible, but you'll likely not really notice any differences in resolution from the regular, 100% setting, but if you can notice it, you'll have a hair more.