the diff vs oneway thing is simple.
myself and every other pro driver run the one way with rubber tires and the diff with foam tires......ALWAYS...
you must set your car up so it handles with the one way if you want to be fast, period.....
with foams there is so much traction that a one way isnt needed and will make your car too twitchy.....
but, when a new car just comes out and a oneway isnt available there are things you can do to the car to make it pretty competitive, but the one way is always faster with rubber....
hope this puts that depate to rest.....