I am running around 300 hp on medium sport tires, I haven't done the refresh yet, but will tonight. As of right now she is just plowing right on through the corners and has some serious lag (which is wierd for a non-turbo car) in the lower gears. I won't have access to the game for a few days so I am sorry I can't give you much more. I guess I was hoping for a 'silver bullet' tune like some of the others offered here.
As an aside, the stock version of this car is handles so close to the real thing it is scary.