an exedy organic has a better more durable friction material and slightly stiffer pressure plate.
stock clutches are designed for normal drivers. not for someone that gets hard on the car.

i dont think that having a flywheel balanced and slightly lightened is any big deal, if they trim just a little from teh backside on the outside edges you should be fine. if you want more than a pounds or two though get a new flywheel that is designed to be lighter.