I can't speak for FSX but in FS9, the following section defines the braking attributes.
[brakes]
toe_brakes_scale = 0.64
parking_brake = 1
differential_braking_scale = 1.0
Reduce the toe_brakes_scale= parameter until you find it to your liking.
Essentially, 1.0=100% and .64=64% of total available braking