Theory behind the upper/lower holes, if you use the upper hole you get more camber gain, meaning as the suspension rises (the wheel rises) the camber increases more than the lower hole. Can give you more grip, to a certain point. Its something to play with if you have a tonne of side bit, and traction roll alot. Ive always used the upper hole, and had the rear as low as possible. Its changing your roll centre, ive seen a website which describes the theory at length. If i find it ill post it!