I ride my rabbits on the single line connection when possible. The weight limit to this setting is 180lbs though...I love this setting 'cause it flies more direct and IMO it's more stable. Otherwise, if I'm flying on bridles it's set to stock setting for the front lines and then fast on the rear lines on all my kites.
"upwind" setting will give your kite a larger turning radius and the "downwind" will make the kite pivot. The best way to feel and see the difference is to do a kiteloop on both settings.