You don't need a parking brake extension if you have an RT-S.
Having finally ridden with the floorboards, I can assure you that it does permit more forward movement of your feet. As a matter of fact, you can even sit comfortably with your leg, above the ankle, touching the brake.
The boards have two possible installation positions, one is at the same place as the original pegs, and the other is about two inches lower than that. I'm using the lower position, since I have a Corbin Lamonster version seat, which is cut deeper (lower) than stock.
For me, these boards are doing just what I wanted them to do.