You are indeed correct Dan but since the downforce is reliant on forward motion, it is safe to assume that there will be a certain amount of downforce at any speed that creates air movement across the wing. Further assuming that downforce will increase by 4.75 pounds for each kph, the answer is easy. If you are losing traction on a slippery road, just increase your speed until the dowforce increases and traction resumes. Now. My discipline was not aerodynamic engineering but this sounds really good anyway....
Hmmmmm..... which gives me another thought.... If one was to drive in reverse at speeds up to 200kph, at what point would the up force on the wing lift the rear of the car off the ground.... Betcha GM hasn't track tested that possibility...