In most cases speed 1 works, it’s already very fast even at 1. In general you have about 150 operating hours on the brushes before they most likely need to be replaced. They are not expensive or hard to get, just no need to wear them out any faster.
Depending on your project, you may want to hog out the material in a roughing cut, then come back in with the more precise tools. Though, obviously this matters depending on what software you have at your disposal.
Most likely the only two setting to mess with would be >>plunge rate<<OOPS:(Meant DOC) and feed rate,
You may want to take a look at this guide: A guide to understanding basic Feeds and Speeds
EDIT: Take easel’s recommendations with a grain of salt for feed and plunge. It seems the type of material affects the values more than the type of bit. So, running through plywood with a 1/8" bit would be fine with the settings, while a 1/32" bit will break. A generic rule is >>plunge<<oops EDIT:(Depth of Cut) value should be 1/2 the bit diameter.