Personally, unless you are going with an aftermarket controller, spider or dccd pro, or something along those lines, I don't think you are getting everything out of a stock set up.
Love my tranny setup now but will admit that it does not work that well on slick ice. Either manual or auto, the front develops a push with non-studded blizzaks that is pretty difficult to overcome. The open differentials of the stock WRX worked better on slick ice. I've yet to try slick ice on a track with studded tires with my new setup.
On every other surface I've experienced so far; snow, gravel, dirt, wet and dry pavement, the dccd works better. I will also say that personally, unless you are competing with your car, it is all a waste of money that could be better spent elsewhere first. It may function and assist but these cars are so good without dccd, it really is overkill. Just more gadgets that can break.
Merely my opinion.