I run square tyres and wheels on my e46 m3 - it means I can rotate tyres to get more life from them and because the fronts are now wider, I can brake harder, I can dial out the under steer more and I make fewer tyre screechy noises.
If I were the OP though, why not do a couple of days on stock sized wheels and tyres, review what you think the problems are, and then resolve using your own info. So much of what everybody says is specific to driving style, experience, car setup, etc.. that what works for one person may not be as good for another.