I put a set of Dunlop winters on our c55 last year and frankly I was disappointed. I expected not to notice the snow but I couldn't even get off the drive! This is the same drive that our old imprezas on summers sailed up and down with apparent impunity in those conditions. Once up and about there were no dramas but I have no idea if I would have been more slidey on the summers.
I've always wondered how just rubber compounds make "that" much difference but general opinion seems to be that it does. My experience was not positive.
I have just put a set of Vredstein Quadtrac 5 on my old RR but I have only done about 5 miles since so its a tad too early to say. And quick it is not.