As I said, the search function will help here, but in a nutshell, the braking advantages seem to be associated with reduced fork stiction which improves suspension performance under braking loads as the forks are pushed away rather than tucked under the bike.
The main benefits people seem to note have more to do with handling. By moving the caliper weight behind the forks and down, it seems to improve stability to some degree, to the point of possibly reducing the chance of headshake problems, and perhaps also reducing any wheel flop tendencies. I know my bike felt a bit more surefooted after I made the change and when I roll with my hands off the bars now, she tracks nice and true and steady.
A side note to this is that ALL modern bikes including the late 70's Honda's and onward position the brake calipers behind the forks. If on top and ahead was the right way, then that's how they'd be done.
tony
