The same length as a piece of string. it depends entirely on the type of mileage the car does - lots of stop-start city driving, motorweay driving, short distance long distance, a drive who is heavy on gear changes, rides the clutch - the list goes on, and all these variables make a stock answer very difficult to find.
Why not ring around a few Ford dealerships and ask their mechanics about Galaxy clutches - maybe you can get some idea from what they advise.