Originally Posted by Geoff-AU

Fluids are incompressible. In terms of static system (holding the pedal down constantly) you will feel the same force at the same pedal displacement.

The only difference is in dynamic feeling. A really viscous fluid doesn't want to move. This suggests it will give you a rock hard pedal feel right away and then the pedal will gradually sink until it stabilises, during which time you get less braking effort than you feel on the pedal. You probably won't notice the pedal travel, because what you feel is the pressure on your foot.

A less viscous fluid will give you more pedal travel with low resistance but then it will firm up really quickly. That initial pedal travel probably explains the "my brakes aren't there" feeling people don't like. You always have to move the pads a little bit in order to make them bite on the rotors so there must be some pedal travel.